Was Lupin truly a great professor?

The Reveal of a Secret 1

Introduction

A while ago, I published an essay that discussed the events of the Shrieking Shack. Since explaining everything would have taken an hour long, we decided to focus on Sirius and finished by hinting that Professor Lupin had fucked up. And here’s the day we will explain it all! Let me show you why Remus Lupin is in canon, not the great professor you might have thought he was when watching HP3. 

Confess the Truth

A schoolboy mistake

Let’s start from where we left last time, at the Shrieking Shack; more precisely, the moment Snape enters the room under the Cloak of Invisibility and waits as Lupin tells his story. A story that we could have been spared from and which seemed to have nothing to do with Scabbers by the way:

Harry couldn’t see where this story was going, but he was listening raptly all the same.

And I couldn’t either; nonetheless, I’ll summarize what Lupin tells us:

1) He has been a werewolf since he was a child, and he used to become “a fully-fledged monster once a month” as Wolfsbane hadn’t been invented yet.

2) The Headmaster managed to get Lupin education at Hogwarts by making arrangements for him; those were imperative to follow so he wouldn’t endanger anyone. Dumbledore constructed the Shrieking Shack near Hogsmeade and out of bounds from Hogwarts, created the tunnel leading to it, planted the Whomping Willow at the beginning of the tunnel so nobody would enter and meet Remus Lupin as a werewolf, and had Pomfrey take special care of him, so he could transform in a safe place. Dumbledore also encouraged the rumor that there were violent spirits in the Shack to cover the story and avoid the reveal that there was a werewolf in Hogwarts, effectively protecting Lupin’s identity.

3) This is where Lupin’s long-term history of fucking up begins. He admits that he led his three friends to become Animagi illegally, unsupervised, despite how dangerous it can be to attempt to become an Animagus. They achieved it by fifth year, meaning, the year Lupin became a Prefect. [“Finally, in our fifth year, they managed it. They could each turn into a different animal at will.”] Then, every month at night, for years, using the Cloak and their illegal Animagi forms, they sneaked out of their beds and entered the Shack in which Lupin transformed. [“They sneaked out of the castle every month under James’s Invisibility Cloak. They transformed… Peter, as the smallest, could slip beneath the Willow’s attacking branches and touch the knot that freezes it. They would then slip down the tunnel and join me.”] 

4) They didn’t do just that. They managed to get werewolf Lupin out of the Shack that had been constructed for the express purpose of protecting Lupin and all those outside. Moreover, they had him wander the Hogwarts grounds and Hogsmeade for the following hours. The HP fandom believes they only had Lupin wander the forest–which is still dangerous by itself (remember the Acromantulas?)–and yet, Lupin states it clearly: “Soon we were leaving the Shrieking Shack and roaming the school grounds and the village by night.” The problem? 

“Running around in the dark with a werewolf! What if you’d given the others the slip, and bitten somebody?” 

“A thought that still haunts me,” said Lupin heavily. “And there were near misses, many of them.”

5) So by now, Lupin knows that he and his friends put countless people in danger of being mauled to death or infected by a werewolf, and for a fact: there were many near misses, meaning that at several points it was shown that with a little less luck (or rather, a little less plot armor), a tragedy would have occurred. That if someone didn’t die, then another werewolf could have been born. Plus regardless that werewolves don’t attack Animagi, Lupin could have known that it was still incredibly dangerous for his “thoughtless” friends, as they could have been severely wounded or even killed by his werewolf form if, for instance, they frustrated him too much or were too rough on him. Just look what happened to Sirius in Harry’s 3rd year. And yet…

6) Lupin betrays Dumbledore, Pomfrey, and all those who were working for his protection:

“I sometimes felt guilty about betraying Dumbledore’s trust, of course… he had admitted me to Hogwarts when no other headmaster would have done so, and he had no idea I was breaking the rules he had set down for my own and others’ safety. He never knew I had led three fellow students into becoming Animagi illegally. But I always managed to forget my guilty feelings every time we sat down to plan our next month’s adventure. And I haven’t changed…”

Lupin knew all along that these monthly excursions were an issue that couldn’t be allowed any longer, but he enjoyed the adventure too much to put an end to it. He could have kept to his responsibilities as a Prefect who knows how terrible it is to be attacked and suffer as a werewolf. He could have told Dumbledore their secret: given the amount of privilege the Headmaster has offered him and his friends [“He let me into Hogwarts as a boy, and he gave me a job when I have been shunned all my adult life, unable to find paid work because of what I am.” + Prefect + Head Boy], surely he could have let them keep company with Lupin while making the whole thing safer by having a teacher watch over them. But it was too fun to do it all in secret… even if it meant the lives of his peers were on the line.

Lupin has gravely broken safety rules during his school years. But very well; due to plot armor and moral luck, no one was hurt, and it’s all in the past, so surely we can do as if it didn’t matter?

7) Unfortunately, it does; Lupin makes it matter, years into adulthood:

“All this year, I have been battling with myself, wondering whether I should tell Dumbledore that Sirius was an Animagus. But I didn’t do it. Why? Because I was too cowardly. It would have meant admitting that I’d betrayed his trust while I was at school, admitting that I’d led others along with me… […] And so I convinced myself that Sirius was getting into the school using dark arts he learned from Voldemort, that being an Animagus had nothing to do with it…”

So let me get this straight. In Prisoner of Azkaban, Dumbledore hires Lupin as a professor and allows him to live at Hogwarts, which means getting a stable revenue, a relatively stable home, friendly colleagues and students to keep him company, a nurse and a potions master to give him his meds and care for him, as well as regular, healthy meals. He gets a teacher—Professor Snape, who hates Lupin, for valuable reasons—to brew him Wolfsbane monthly, an incredibly complicated and expensive potion offered by the school [However, the Wolfsbane Potion was complex and the ingredients very expensive], that allows Lupin to transform safely and sleep the full moon in his office while retaining his human mind, instead of having to do it in a lone cold Shack like before. Dumbledore spends the year protecting Lupin, nevermind people have been calling him mad for hiring a werewolf at Hogwarts:

“Dumbledore hired you when he knew you were a werewolf,” Ron gasped. “Is he mad?” 

“Some of the staff thought so,” said Lupin. “He had to work very hard to convince certain teachers that I’m trustworthy —” 

Lupin knows this, by the way:

“Professor Snape […] fought very hard against my appointment to the Defense Against the Dark Arts job. He has been telling Dumbledore all year that I am not to be trusted.”

And how does Lupin return the favor? How does he plan to prove Professor Snape wrong?

He keeps vital information from Dumbledore–his employer, the leader of the Order, his protector–just because he was too cowardly to admit that he’d been… a bad student. As if Dumbledore didn’t already know Lupin had been a poor Prefect in the first place.

And I haven’t changed…

Why is it so important, you’ll ask me, that Lupin hasn’t told Dumbledore that Sirius Black was a dog Animagus? Because you’ve got to look into the context and what it means.

The movie has Harry tell Professor Lupin that he saw Pettigrew on the Map midway through the year, so Lupin knew for quite a few months that Pettigrew was alive and as such, he could suspect Sirius Black was innocent. Lupin confirms it again in the Shack. From what he says and the way he behaves, there’s no doubt that he already knows the truth. He doesn’t need Sirius to confirm if Pettigrew was the true Secret Keeper and thus the traitor. That makes the whole plot stupid because it means that Lupin left Pettigrew unpunished and Sirius desperate in the cold outside for months, for no apparent reason. Movie!Lupin was an unloyal, shitty friend to Sirius. Funnily enough, some fans argue that in book-canon, Lupin suspected all along that Pettigrew was the traitor and Sirius the innocent man, so they’re basically arguing that Lupin left Sirius Black to rot in Azkaban for more than a decade even though he could have done something for his old friend. Arguably worse. In the novels however, Lupin actually says:

“Everyone thought Sirius killed Peter,” said Lupin, nodding. “I believed it myself — until I saw the map tonight.”

What does that tell about him? 

In the books, during this whole year, until this night at the Shack, Lupin wholeheartedly believed that:

1. Sirius Black was a servant of Lord Voldemort (ie a Death Eater)
2. That he betrayed the Order and murdered James and Lily
3. Murdered Lupin’s best friend Peter, who was blasted to bits in the attempt to stop Sirius Black
4. Murdered 12 Muggles in the process (and laughed like a maniac)
5. Managed to do the impossible and escape Azkaban using extremely powerful Dark Arts
6. Was set on killing James and Lily’s son in Hogwarts.

Furthermore:

7. There’s record of Sirius attempting to murder teen Snape using Lupin’s lycanthropy, or alternatively, both were almost guilty of manslaughter because of him
8. Lupin witnessed the portrait of the Fat Lady torn apart after Sirius Black savagely trashed it, trying to enter Gryffindor Tower and seemingly attempting to kill a sentient portrait when it wouldn’t give him access (that’s why the Fat Lady had to be restored)
9. He knows that Sirius finally managed to enter the 3rd year Gryffindor dormitories during the night, stood over a child’s bed and slashed its curtains with a twelve-inches long knife, so a student was almost killed (a traumatizing event, Hermione cried because she thought Sirius tried to stab Ron to death)
10. Basically every child at Hogwarts, every one of Lupin’s staff colleagues, and every person in Hogsmeade was in mortal danger (or at the very least, potential mortal danger, which is more than enough).

Lupin had every reason to share that type of crucial information with Dumbledore. But!… he doesn’t do it. As metametatron4 says in Fanon vs Canon: Remus Lupin Edition:

In Lupin’s own words, he selfishly prioritized his own good standing with Dumbledore and good reputation over the lives of all the children at Hogwarts, including Harry. Lupin enjoyed his popularity as a well-liked teacher, but when it came to the students’ safety, he floundered. He « convinced himself » with the lie « that Sirius was getting into the school using dark arts he learned from Voldemort, that being an Animagus had nothing to do with it » when he knew better. But this lie doesn’t make Lupin any better. In some ways, it makes him worse because he operates under the pretense that Sirius learned dark arts from Voldemort that are so powerful they can break through Hogwarts’ protective enchantments and extra security, yet he doesn’t tell Dumbledore about the secret passages to take a partial protective measure against Sirius. He sticks his head in the sand.

Additionally, Lupin knows that more than a hundred Dementors had been posted around Hogwarts in the frantic attempt to stop Sirius:

• Before he’d had time to think, Harry had taken his eyes off the Snitch and looked down. At least a hundred Dementors, their hidden faces pointing up at him, were standing beneath him. […]
• Dementors, at least a hundred of them, gliding in a black mass around the lake toward them.

He knows that they have devastating effects on people, particularly those who have trauma like Harry:

“Dementors are among the foulest creatures that walk this earth. They infest the darkest, filthiest places, they glory in decay and despair, they drain peace, hope, and happiness out of the air around them. Even Muggles feel their presence, though they can’t see them. Get too near a Dementor and every good feeling, every happy memory will be sucked out of you. If it can, the Dementor will feed on you long enough to reduce you to something like itself — soul-less and evil. You’ll be left with nothing but the worst experiences of your life.” 

In fact, he saw the effect it had on Harry:

Harry felt his own breath catch in his chest. […] Harry’s eyes rolled up into his head. […]

“I thought you were having a fit or something,” said Ron, who still looked scared. “You went sort of rigid and fell out of your seat and started twitching —” 

He witnessed it twice; remember Harry’s Quidditch match against Hufflepuff:

“I thought he was dead for sure.”

[…] “You fell off,” said Fred. “Must’ve been — what — fifty feet?”

If we count the Boggart Dementors that he used to train Harry for the Patronus, then Lupin witnessed it many, many times. As Lupin puts it:

“And the worst that happened to you, Harry, is enough to make anyone fall off their broom.”

Then Harry tells him what happens in his head whenever a Dementor approaches him:

“When they get near me —” Harry stared at Lupin’s desk, his throat tight. “I can hear Voldemort murdering my mum.”

Overall, it’s not for nothing that Dementors are used in Azkaban:

“Azkaban must be terrible,” Harry muttered. Lupin nodded grimly. 

“The fortress is set on a tiny island, way out to sea, but they don’t need walls and water to keep the prisoners in, not when they’re all trapped inside their own heads, incapable of a single cheery thought. Most of them go mad within weeks.” 

Everyone knows they are dangerous for the students too:

“It is not in the nature of a Dementor to understand pleading or excuses. I therefore warn each and every one of you to give them no reason to harm you. I look to the prefects, and our new Head Boy and Girl, to make sure that no student runs afoul of the Dementors,” he said. 

They could attack a child in Hogwarts, like they tried to do with Harry and Hermione at the end of PoA. If not, Pomfrey still affirms:

“Setting Dementors around a school,” she muttered, pushing back Harry’s hair and feeling his forehead. “He won’t be the last one who collapses. Yes, he’s all clammy. Terrible things, they are, and the effect they have on people who are already delicate —” 

So Lupin knew his students were more or less being tortured by the Dementors. The quicker Sirius Black was captured, the sooner the danger would go away… But Lupin does… nothing.

Wait, perhaps he just didn’t want Sirius to be Kissed by the Dementors if he was captured!

And I’ll have to disagree. When it is revealed that Pettigrew had been the traitor all along instead of Sirius, Lupin was ready to murder him on the spot:

“You should have realized,” said Lupin quietly, “if Voldemort didn’t kill you, we would. Goodbye, Peter.” 

When Harry suggests they throw Peter into Azkaban or to the Dementors, Lupin doesn’t protest at all. 

“We’ll take him up to the castle. We’ll hand him over to the Dementors… He can go to Azkaban… but don’t kill him.” […] 

“Very well,” said Lupin.

He looks like he might criticize the use of the Dementor’s Kiss upon people [“Do you really think anyone deserves that?”], but it’s all for show. In the end, he’s just like the others; using Dementors on a convicted criminal is okay for him. Killing one himself in front of 3 children is okay too. He’s the one after all who advises Harry to kill his enemies in DH, even the Imperiused (which Harry refuses). Keeping Sirius’ secrets never was an act of kindness, it was a selfish attempt to protect his own reputation.

I would even argue that it was in Sirius’ best interests for Lupin to tell Dumbledore the crucial piece of information about his Animagus form. He could have asked Dumbledore to give Sirius Black the benefit of the doubt when they caught him–all the more so if he suspected that Sirius was innocent. Dumbledore is a smart general of war, a fierce anti-Voldemort fighter and has been vouching for Lupin all along–he’s protected Sirius when he’d almost killed Severus years ago, for God’s sake! There was little doubt Dumbledore would follow Lupin’s advice, if he didn’t think about it on his own. They could have worked together to save Sirius from his misery and make Pettigrew meet justice. But Lupin didn’t even try. For which reason? Oh yeah, he was too cowardly to admit he’d failed Dumbledore as a kid.

It’s such a shame, because if Lupin had admitted his mistakes to Dumbledore, not only would it have meant he truly became a better man, but it would have been rather heroic. He could have been forgiven on the spot if he’d admitted his mistakes for the sake of the children. 

The sad truth is that Lupin never changed through all these years. He would always remain a cold-hearted, selfish coward. Including years after PoA when his own child and his wife were on the line.

As long as he protects his image, he gladly lets hundreds of children in mortal danger, notably the orphaned son of his deceased best friends. He leaves them and all the people in Hogsmeade suffering the Dementors, which is equally as bad. Hogwarts School of Witchcraft and Wizardry has become the new Azkaban, and Lupin couldn’t give a shit. Dammit, Severus Snape is a nasty teacher, but at least he never gambles with the lives of his students just to preserve his popularity with the facade of a nice guy! 

I rant about Lupin failing to tell Dumbledore the truth about Sirius’ status as an unregistered Animagus, but there are two other facts that Lupin could have shared:

• First, Sirius’ boyhood knowledge of all the secret passages into the school.

Lupin could have told the Headmaster that Sirius knew all the secret passages of Hogwarts–possibly, passages that Dumbledore didn’t suspect existed. They could either shut them down for the school’s safety or put traps in there to catch Sirius without the Ministry or the Dementors interfering. He doesn’t.

• Second, the existence of the Marauder’s Map.

The Marauder’s Map could be used to watch over Hogwarts and for future break-ins from Sirius Black. This way, Dumbledore and Lupin could have caught him easily and sooner. (Dumbledore has great Disillusionment abilities.) He doesn’t. And I’ll show you why it’s so infuriating. 

Harry has got hold of the Map at some point in the story, and managed to get to Hogsmeade thanks to it, alone, without the protection of the Dementors, without the professors’ knowledge… let alone their agreement. In a nutshell, Snape catches Harry first, Lupin intervenes, confiscates the Map and scolds Harry when they’ve gone far enough from Snape’s office:

“I don’t want to hear explanations,” said Lupin shortly. He glanced around the empty entrance hall and lowered his voice. “I happen to know that this map was confiscated by Mr. Filch many years ago. Yes, I know it’s a map,” he said as Harry and Ron looked amazed. “I don’t want to know how it fell into your possession. I am, however, astounded that you didn’t hand it in. Particularly after what happened the last time a student left information about the castle lying around. […] Don’t expect me to cover up for you again, Harry. I cannot make you take Sirius Black seriously. But I would have thought that what you have heard when the Dementors draw near you would have had more of an effect on you. Your parents gave their lives to keep you alive, Harry. A poor way to repay them — gambling their sacrifice for a bag of magic tricks.”

…The fucking hypocrite. So Lupin was well aware how scandalous it was to conceal such valuable information and items: he sets those standards himself. Contrary to Harry, who’s just being an idiotic, frustrated teenager, Lupin is a 33 years-old adult in charge of protecting the children. He is the Defense teacher. Nonetheless, he has the gall to use his student’s confession about what the Dementors do to him and turn it against him, apparently wishing it traumatized the boy even more; then he shames Harry in a shockingly cruel way by guilt-tripping him with the death of his parents… While HE is currently wasting James and Lily’s sacrifice for an irrelevant, two-decades old, schoolboy mistake.

So let’s sum it up.

“All this year, I have been battling with myself, wondering whether I should tell Dumbledore that Sirius was an Animagus. But I didn’t do it. Why? Because I was too cowardly. It would have meant admitting that I’d betrayed his trust while I was at school, admitting that I’d led others along with me…”

Lupin effectively places the value of his nice facade above the lives and welfare of the children. He contributes, with his refusal to share pertinent pieces of information, to the mortal endangerment and trauma of countless people. Through his inaction and his repeated lies, Lupin effectively allows a believed terrorist to break into Hogwarts unchallenged. Had Sirius genuinely been Harry’s enemy, the consequences of Lupin’s self-interest could have been disastrous. 

Now imagine you’re a parent, and you learn that a teacher has performatively allowed a serial killer to repeatedly enter the school your child attends to, nevermind that your baby is being tormented by said killer (and the Dementors), or that it was the teacher’s duty to protect the children as much as he could. Lupin has profoundly failed his charges as a teacher, and is responsible for the suffering and the near-death of many. Do you think such a teacher deserves to hold their post any longer? I’d say that there are very good reasons to fire him. And if any of the children or the staff had come to harm, a trial would be waiting for him. Well, in the Muggle world at least. 

Running around in the dark

Let’s speed up a bit in time and get to the other major reason that Lupin couldn’t remain a teacher. Mainly… his transformation into an unmedicated werewolf out in the open.

Careful there. I’m not saying that Lupin couldn’t have remained a teacher for the simple fact he’s a werewolf, that’s bullshit. What I’m saying is that Lupin’s carelessness and irresponsibility could have resulted in the death, incapacitation or infection of many people, and in particular, Harry, Ron, Hermione, Sirius, Severus and… well, Pettigrew, if we want to be exhaustive. We could also count future Harry and Hermione, as well as anybody that Lupin might have encountered on the Hogwarts grounds or in the Forbidden Forest (like Hagrid). 

“Hermione!” said Harry suddenly. “We’ve got to move!” 

“We mustn’t, I keep telling you —” 

“Not to interfere! Lupin’s going to run into the forest, right at us!” 

So that’s at least 3–or 5?–students, two Hogwarts professors and two other men. Lupin is extremely lucky that nobody was harmed. Or, well, almost nobody (Sirius got bloodied). Why did this happen? 

Lupin was allowed to teach at Hogwarts on the condition, of course, that he never put the children in danger by himself with his lycanthropy. During the year, he has been offered Wolfsbane:

“Professor Snape has very kindly concocted a potion for me,” he said. “I have never been much of a potion-brewer and this one is particularly complex. […] This potion is the only thing that helps. I am very lucky to be working alongside Professor Snape; there aren’t many wizards who are up to making it.” 

As far as we know, Snape wasn’t obligated to offer Wolfsbane at all. He could have decided that Lupin could very well manage on his own, which means transforming in the Shack and suffering like before. Regardless, he relieves Professor Lupin of his pain and ensures his worst nightmare (“It had always been Remus’s worst fear that he would kill while out of his right mind”) will not become true. Snape gave Lupin what the other Marauders could never achieve: a safe and painless night at the full moon. Lupin acknowledges three years later that it was a very kind courtesy from Professor Snape:

“[…] I do not forget that during the year I taught at Hogwarts, Severus made the Wolfsbane Potion for me every month, made it perfectly, so that I did not have to suffer as I usually do at the full moon. […] He kept me healthy. I must be grateful.”

I could bet a thousand Galleons that werewolves would kill for the chance to drink Wolfsbane.

“The potion that Professor Snape has been making for me is a very recent discovery. It makes me safe, you see. As long as I take it in the week preceding the full moon, I keep my mind when I transform… I’m able to curl up in my office, a harmless wolf, and wait for the moon to wane again.” 

This passage is a bit ambiguous. Does Lupin mean that he has to take Wolfsbane every day of the week preceding the full moon (as fandom wikia suggests)? Or does he mean that as long as he takes it at least once in the week prior to his transformation, he will become a harmless wolf? Fortunately, I found this quote about Wolfsbane:

“I made an entire cauldronful,” Snape continued. “If you need more.” 

“I should probably have some again tomorrow. Thanks very much, Severus.”.

So it rather sounds that as long as Lupin drinks Wolfsbane in sufficient amounts at least once in the week that precedes his transformation, it’s all good. The reason he doesn’t want to drink all at once seems to be due to the Wolfsbane’s disgusting taste. 

He picked up the goblet and sniffed it. “Pity sugar makes it useless,” he added, taking a sip and shuddering. […] Lupin drained the goblet and pulled a face. “Disgusting,” he said. 

Meaning that Lupin had a whole day–and in fact, a whole week–to take his dose of Wolfsbane. However, what was he doing at the time he was absolutely meant to drink it? Ah yes. Reading a map calmly in his office. For more than twenty minutes. He wasn’t even working, and not the least concerned that the moon was already rising. 

“I watched you cross the grounds and enter Hagrid’s hut. Twenty minutes later, you left Hagrid, and set off back toward the castle. But you were now accompanied by somebody else. […] I couldn’t believe my eyes,” said Lupin, still pacing, and ignoring Harry’s interruption. “I thought the map must be malfunctioning. How could he be with you?”

Instead, it is Severus who has to bring Lupin’s Wolfsbane:

“I’ve just been to your office, Lupin. You forgot to take your potion tonight, so I took a gobletful along.”

This isn’t the only time this has happened, it started from the very beginning of the year:

“Ah, Severus,” said Lupin, smiling. “Thanks very much. Could you leave it here on the desk for me?” Snape set down the smoking goblet, his eyes wandering between Harry and Lupin. […]

“You should drink that directly, Lupin.” 

“Yes, Yes, I will,” said Lupin. [He won’t until Severus leaves the room]

It’s fair to assume that this wasn’t a two time occurrence; it’s likely been going on for a year. Severus doesn’t have any obligation, as far as I recall, to bring Lupin his own medication. It’s good enough that he brews him cauldronfuls of Wolfsbane, he shouldn’t have to serve Lupin in his own office as if he were his House Elf (with all the respect for those Elves who don’t deserve this slavery). I suspect that Lupin was quite enjoying this passive-aggressive power-play. And if that’s the case, it means that not only was Lupin being super negligent and lazy about his medication, but also that he was playing with a condition that represented a real, grave danger to the students and the staff, just so he could silently torment a man he owes, for the sake of good ol’days. A man who makes the effort to brew Lupin a very complicated but revolutionary and life-changing potion, and who Lupin personally knows was traumatized by him and his friends by a werewolf who tried to maul him as a teen (the Werewolf Incident). 

Lupin hasn’t moved his ass for 7 days to get his Wolfsbane, and this level of negligence is so absurd that Snape must assume Lupin has forgotten it the night of his transformation as well. (It is so absurd that the fandom assumes that Lupin must have forgotten to take his meds once in a 7-days treatment, rather than to take it at all during the course of an entire week!) The moon is rising and a fellow professor must again bring him a gobletful of Wolfsbane so werewolf-Lupin doesn’t run out of his office to make a rampage throughout the school. That’s already a huge red flag, which at best would have earned Lupin a warning, and at worst, a dismissal with a very bad remark on his career file.

Now, people argue that it was Severus’ fault that Lupin couldn’t drink his Wolfsbane in the Shack. However, could you tell at which point in the story is it said that Professor Snape was Lupin’s baby-sitter?

…Not accounting how difficult it would have been for Severus to

• sprint down several sets of stairs down the castle and through the grounds
• manipulate a branch, a cloak, a wand and a goblet at once to touch the knot of the Willow, cover himself with the cloak and rush through a cramped tunnel up to the Shack
• keep Sirius and Lupin in check with his wand while simultaneously forcing the Wolfsbane potion down Lupin’s throat
• all the while without making the potion tip over the goblet too soon;

I will also argue that it was, in fact, a safe measure that Snape took when he didn’t bring Lupin his Wolfsbane. Remember what this potion does:

“As long as I take it in the week preceding the full moon, I keep my mind when I transform… I’m able to curl up in my office, a harmless wolf, and wait for the moon to wane again.”

Wolfsbane does not prevent a man from transforming into a werewolf, it only allows him to retain his human mind. If Lupin was, as Snape believed, intent on killing the Trio with Sirius Black, then making him drink Wolfsbane would only give human intelligence to a wizard with murderous goals. And what’s more dangerous than a feral werewolf? An intelligent werewolf. Considering Snape could rightfully suspect Lupin was the accomplice of a convicted murderer, it would have been a huge mistake to bring the potion. Snape could also have assumed that Lupin would resist taking it anyway, choosing to be mindlessly savage for murder, making the whole struggle of bringing Wolfsbane over with him useless. Nevertheless, it was Lupin’s responsibility to drink it earlier, because contrary to Snape, he knew he was on Harry’s side.

But I see you coming. This was a one time mistake! Ignoring for a moment that it was a week-long mistake, it doesn’t change much because it only takes one mistake to do a massacre, and one time is enough to get Lupin sacked. Because you know what’s worse? 

As soon as the moonrays hit Lupin directly, he transforms into a werewolf:

A cloud shifted. There were suddenly dim shadows on the ground. Their party was bathed in moonlight. […] Harry could see Lupin’s silhouette. He had gone rigid. Then his limbs began to shake. 

We know Lupin can indeed transform inside the Shack:

“Once a month, I was smuggled out of the castle, into this place, to transform. […] My transformations in those days were — were terrible.”

He has been staying in the Shack for around two hours, during which at any moment, Lupin could have transformed, as the moon certainly had risen:

“We need to wait until they’ve gone back to the castle. Then we wait until it’s safe to fly Buckbeak up to Sirius’s window. He won’t be there for another couple of hours…” […]

The only reason Lupin didn’t transform until he… actually did, is because clouds were covering the sky:

“Here comes Lupin!” said Harry as they saw another figure sprinting down the stone steps and halting toward the Willow. Harry looked up at the sky. Clouds were obscuring the moon completely. […]

The moon slid out from behind its cloud. They saw the tiny figures across the grounds stop. Then they saw movement — 

“There goes Lupin,” Hermione whispered. “He’s transforming.”

However, it should be noted that the moon wasn’t hidden behind clouds all the time. Indeed:

The moon drifted in and out of sight behind the shifting clouds.

The result? Remus Lupin should have already transformed into a werewolf in the Shrieking Shack and potentially lead to a carnage (Ron half eaten; Hermione mangled; Harry infected; Snape scarred; Sirius dismembered; to name a few examples). The only reasons that didn’t happen is, I guess, because 1) clouds were hiding the moon, 2) the moon was angled so that its light couldn’t directly reach Lupin in the Shack yet, 3) Rowling suddenly put new rules in place that make the plot incoherent. Indeed, why does Lupin ever have to transform – why were his friends needed to become Animagi to relieve him – if all he needs is to hide in a room that shields him from the moonlight to avoid transformation?

Remus Lupin didn’t become someone’s killer thanks to pure, dumb luck and a plothole. Had JKR well constructed HP, then Lupin should have reduced his students, his colleague and his friend to bloody pieces. Alternatively, since we know the moon was already up by the time Lupin was sprinting to the Willow, it means that he could have transformed either inside the castle or on the school grounds before ever reaching the Shack.

It also confirms that Snape could expect a fully transformed werewolf when he went to save the children in the very place he was nearly mauled to death by a werewolf as a teen. 

(As an aside, the real full moon of June 1994 was on Thursday the 23rd, and it was up since 1:33 pm, so Lupin should have transformed way earlier, not just during the night. Then again, the « werewolf transforms on a full moon » plot in Harry Potter is very poorly executed. For instance, Lupin took his Wolfsbane on the 31st of October and transformed « a few days later », between the 5th and the 7th of November 1993. However, according to real-world moon cycles charts, he should have transformed on the 30th of October, while the 7th of November was a last quarter moon, which means that Lupin doesn’t follow our moon cycles. Yet we’re left to believe that Lupin also transformed around Christmas of that year, which would be the 29th of December 1993 in the real world, and on a Thursday of June 1994, which is supposedly the 23rd. So unless Lupin actually transformed on the 5th of January 1994 and was « tired » two weeks before the transformation, and unless the Thursday of Pettigrew’s escape in June was the 30th instead of the 23rd, then Lupin’s transformation cycles are inconsistent, varying between fitting real-world moon cycles and fiction moon cycles (that would match real-world quarter moons). Thus I guess it’s way too much to ask to have Lupin actually transform whenever the full moon rises, which would include during the day, and for more than a single night since a full moon can last up to three days to the naked eye. Unless we want to be strict and consider that a full moon only technically lasts an instant, meaning that there shouldn’t be any lasting transformation at all, or, in case the full moon rather acts like a trigger, that as long as he remains hidden from moonlight in the split second where it’s truly a full moon, he could avoid it altogether and enjoy the rest of the night. Here and here for additional explanation.)

What should Lupin have done, considering he hadn’t drunk his potion yet and that some form of godly plot armor was preventing him from transforming inside his office? Simple: when he saw what was happening within the Map, he could have alerted the Headmaster with a Patronus, which we know he’s able to cast, and told him to go into the Shack in his place, knowing that he was too much of a danger to go help the Trio. I’m sure things would have been way more straightforward if Albus Dumbledore had been confronting Pettigrew…

So that’s two missed solutions down the hole, and here’s the last one: by the time he knew he would transform any moment now that the full moon was up, Lupin should have stayed in the Shack while the children were secured away. He’s spent his childhood years transforming inside it; there’s a big drama revolving around his lycanthropy; he reminds everyone that he used to transform here; he talks about the Werewolf Incident and the old night excursions; Severus reminds him that he didn’t drink his Wolfsbane tonight; yet for some reason he’s not transforming, so the Shack seems to be relatively good protection, at least for now. But nope! Let’s get out of the Shack during the full moon. And don’t Petrify Peter or Mobilicorpus him up to the castle like you do to Snape, you must keep the plot stupid! Instead, make a child with a broken leg walk shackled to a mass-murdering Death Eater who can escape by transforming into a rat.

Lupin proved that he couldn’t handle his illness responsibly (let alone the transfer of a criminal). Without the insane amount of moral luck displayed here, the Defense professor of Harry’s third year would have caused a disaster.

“I could have bitten any of you… That must never happen again.” 

Conclusion

Does Lupin deserve to be fired just because he’s a werewolf? Nah. But it’s fair to say he doesn’t deserve to remain the Defense Professor after all the ways he has failed his teacher duties. Not only has he kept vital information from his superior despite patently knowing that it basically consisted in covering up for a child-murdering terrorist; not only has he been extremely neglectful about his medication for a long period of time; but Professor Lupin did not remain in the Shrieking Shack when he should have, as it was required of him not to ever put the children in mortal danger. It is a fact that hadn’t Rowling been so intent on showering him with moral luck–then Remus Lupin would have killed, incapacitated or infected the students he was meant to protect, as well as his old friend and the man who gave him Wolfsbane all this year precisely to prevent this. And Pettigrew could have become a werewolf too, I guess… (Imagine a Ron tombstone… Hermione disfigured/blind… Harry as a tame werewolf that needs Snape’s Wolfsbane till year 7…)

Just a tiny changement could have tipped the scales:

• if Sirius had severely harmed or even killed somebody in his unhinged state (like when he strangled Harry),
• if Sirius had been a true Death Eater, 
• if the Dementors had succeeded at getting someone killed (when Harry fell off his broom, when he nearly got his soul sucked off twice)
• if clouds weren’t hiding the full moon
• if moonlight had triggered Lupin’s transformation even if indirectly
• if the plot had been coherent and Lupin had transformed in his office, on the school grounds or in the Shack at the full moon just like he always used to…

…then the worst could have happened.