(A/N: This is a quick idea that wouldn't leave me alone. I have a very high opinion of McGonagall, and while she's a stickler for rules, I think she knows the right time to break them.)
James was chosen for the task, because he was a better dissembler than Peter and had a reputation for being somewhat more responsible than Sirius. The end of Friday afternoon's Transfiguration lesson was chosen for the time. They had reasoned that McGonagall would be the most receptive to having a chat with a student then, as it was the end of the week and she had a free period before dinner so there would be no need to rush anywhere. They waited two weeks after McGonagall had revealed her ability to turn into a tabby cat. Any longer and it would have seemed unlikely that James' interest had been genuinely sparked by seeing her transform, but it took the whole two weeks to build up the goodwill they felt was necessary for the attempt. James had been paying attention in class, he had perfectly transfigured a hedgehog into a pincushion, and he had twice been observed telling Sirius and Peter to stop goofing off. The original plan had been for all three of them to go on their best behavior, but on reconsideration they had realized this was too suspicious; better to make sure McGonagall saw James scolding the other two.
Remus had watched the whole thing with an air of bemusement, clearly torn between approval of James' behavior and deep suspicion as to the cause. James felt uncomfortable leaving him out, but they had agreed there was simply no way they could tell Remus about their idea unless they were certain it would work. It would be cruel to make him hope for something and then find out they couldn't do it.
So when the appointed Friday came, James hung back after class (Sirius having been assigned to deal with the potential complication of Remus waiting for him by sweeping their friend out of the room) and approached McGonagall's desk with a carefully composed expression of respect, eagerness, and (he hoped) innocence.
"Yes, Potter?" McGonagall asked, not looking up from her paperwork to see the expression James had worked so hard on.
"Do you have a moment, Professor? I've been thinking a lot about that Animagus thing you showed us."
"I think it's amazing. I think I might want to be one, so I looked at some books but they didn't really tell me everything I wanted to know." That much was certainly true. "Could I ask you a few questions?"
"I am not a substitute for research, Potter."
"I've read everything in the library. I think Madame Pince might have taken out all the books that had real information in them, just in case some dumb kid decided to try it. I mean, you'd have to at least have your NEWT in Transfiguration to do it, I know that much. But I'm still curious, and I figured, how many people get to actually talk to an Animagus when they're learning about it? You probably know stuff that isn't in the books." James made the last comment as offhanded as he could, because McGonagall rarely responded to obvious attempts at flattery.
Whether it was the compliment or having a student's genuine interest in her subject, James knew he was in-McGonagall turned her attention away from the papers she was grading and adjusted her glasses as she looked at him, a sure sign her attention was refocused. "What do you want to know?"
James led with a question he didn't really care about, hoping to further disarm her. "Well, one of the authors talked about having the animal's senses when you're in their body, but the way she said it was confusing. Do you still see things like a human, or would you see black and white if that was what the animal did, or what?"
"You gain the animal's senses, regardless of how different they may be from a human's," McGonagall said. James privately congratulated himself; she was wearing an expression that he recognized as how she looked when she was fully engaged in a lecture, interested in her subject and unsuspecting of any mischief. "However, your brain remains human, and that is likely why the book you read spoke of it in a confusing way. It is confusing, and the great skill of being an Animagi lies in being able to interpret the information from your new senses. Many more people are successful in transfiguring themselves into animals than find they are actually able to use their new bodies."
"So you get the animal's senses but not their instincts, is that it? What about other animals' instincts?" James asked, moving closer to his real question. "Does your behavior or your scent or something let them know you're human?"
"It depends on the animal. Those with more complex brains can typically identify the Animagus in their midst-cats, dogs, owls, etcetera. Those animals with less developed brains will not be able to distinguish between an animal and a transfigured human."
It was time to go for the kill. "What about animals that hunt humans specifically? Like a kappa or a werewolf or an erkling, that sort of thing?" James had practiced nearly a dozen variations of this question on Sirius before deciding that giving three examples, with werewolf in the middle, sounded the least suspicious.
It wasn't enough. McGonagall's expression changed quickly, from "teacher engaged in conversation with interested student" to "teacher detecting student up to no good." James kept his own expression neutral. But McGonagall didn't say anything. The silence lengthened, until James realized that if he really hadn't been hiding anything, he would've been surprised by McGonagall's silence. "Professor, why are you looking at me like that?"
McGonagall's lips thinned. "I don't know," she said evenly, turning away from James and back to her papers.
"You don't know why you're looking at me like that?" James realized as he said it that he sounded cheeky, but it was too late to take it back.
"No, Potter, I mean I don't know the answer to your question. As far as I know, there has never been a study of how Dark creatures react to Animagi. Most Animagi would not volunteer to be the first to find out."
The look she gave him now was positively alarming. As far as James knew the teachers were, so far, blissfully unaware that Remus' friends were in on his secret-but McGonagall's face spoke of grim understanding.
"What about..." James found, to his horror, that he could think of no more questions about Animagi. "What about some book recommendations, then?" he finished weakly.
James relayed the dismal results of the attempt to Peter and Sirius in a whisper later that night in the common room. Not only had they not gotten the information they needed, but it was quiet possible the teachers had just found out exactly how much they knew. Sirius tried to tell James it wasn't his fault, but he still felt very depressed as he headed to bed that night.
With the teachers now completely cut off as a source of information, they had no choice but to actually look for some of the books McGonagall had listed for James. James was right that they were not to be found in the Hogwarts library, but the Black library was another story, and Sirius was able to bully some family member or another into sending him several. Of course they had to hide what they were from Remus-Sirius pulled off a tricky bit of transfiguration and changed the covers to look like comics before he even unwrapped them at the breakfast table.
The books were depressingly dull and, despite being more informative than the ones at Hogwarts, seemed no more likely to answer the question of what a werewolf would do to an Animagus. Peter pointed out that at least they knew how to become Animagi now, but what good would that do, if Remus just ripped them to shreds anyway?
A week after their first conversation, McGonagall told James to stay back after class. Sirius tried to linger, gathering his things slowly, but McGonagall gave him a stern look and he gave up, going out into the hall.
James stood next to McGonagall's desk wearing his best expression of bewildered innocence. He actually hoped she was going to tell him off for something or other, but the sinking feeling in his gut told him it would be about last week. An interrogation into what he knew about Remus? A warning?
"I have spoken to some friends about your inquiry," McGonagall said.
"Your inquiry, Potter. As to whether Dark creatures regard a transformed Animagus as a human or an animal."
"Oh. That. I'd forgotten about that," James attempted.
"Had you? Does that mean you're not interested in the answer?"
"No, I'm still interested," James said quickly.
"I have it on good authority that Dark creatures-including kappa, werewolves, and erklings, as you specified-do not regard transformed Animagi as human. This is not to say that each of those creatures does not present its own set of dangers to other types of animals, which the Animagus should consider carefully before attempting to approach them. For example, kappas may attempt to trick other large mammals as well; and a werewolf might bite an Animagus without the wizard in question contracting lycanthropy, but could still injure it severely with teeth and claws."
"Really?" James fought hard to keep his face neutral. Two emotions were battling for control: elation at the thought that they had finally found something that might let them help Remus, and wariness at how specifically McGonagall had given him the exact information he needed. "Thanks, Professor. You didn't have to go to all that trouble."
"I suspected you wouldn't find the answer in a book." McGonagall turned her attention to the papers on her desk, and James took it as dismissal. He made it all the way to the door before McGonagall's voice rang out. "Potter."
James turned back, one hand on the door handle. "Yes, Professor?"
McGonagall didn't look at him. "You will be careful."
James waited, but she said nothing else. No questions about his motives. No reminders that he was too young to attempt the spell, not to mention the need to register himself if he did.
James thought about saying something about how he'd changed his mind and wasn't interested in being an Animagus. But somehow, he knew it was pointless. So he simply said, "Yes."
"That is all."
James went through the door. Sirius was waiting, looking impatient and anxious. "Does she know?" he asked.
"Actually, it's okay." James grinned at Sirius' skeptical expression. "She's pretending not to know."
True to James' prediction, McGonagall never made reference to the subject again. The first time four exhausted Gryffindors showed up to class the day after the full moon, instead of one exhausted Gryffindor, James thought he saw her smile at him before class began. But it could have been his imagination.