James would've laughed had Sirius not looked like he was about to faint. The idea that Remus, their chocolate-eating, book-loving roommate was actually a vicious man-eating monster was too ridiculous for him to even comprehend. "Sirius…a werewolf? Are you mad, mate?"

"I wish," Sirius replied. "Look, we have to get out of here."

"Is everything all right?" Professor Sinistra was headed in their direction, looking concernedly down at Sirius. "What happened?"

"I think Sirius is sick," said James, thinking quickly. "Can me and Peter take him down to the hospital wing?"

Sinistra took in Sirius's colorless face, his trembling arms and legs, and nodded. "Fine. But I want you two to come right back after."

"Of course, Professor." James and Peter hoisted Sirius up by his armpits and helped him down the tower stairs. They weren't even pretending to have to carry him, really; Sirius's body had gone totally limp.

"Where are we going?" Peter asked.

"Somewhere we can talk," murmured Sirius. "Our dormitory."

So they dragged him all the way up Gryffindor Tower to their room and set Sirius down on the ledge beneath their window. James stepped back, folding his arms over his chest. "All right. Do you care to tell us why you think our roommate is a werewolf?"

Sirius swallowed. "It's the full moon tonight, James. Remus went and got himself trapped in a secret tunnel on the night of the full moon."

"So? Remus is disappearing all the time—it's just a coincidence, mate."

"Yeah, exactly!" Sirius pressed on. "He disappears all the time; like once a month!"

"It is once a month, isn't it?" Peter muttered nervously.

But James still waved them off. "This is ridiculous. Remus doesn't even like when we're mean to Snivellus and his friends. There's no way he's spending full moons ripping little children to shreds with Fenrir Greyback."

"Well, that's why he's trapping himself underground!" said Sirius. "So he doesn't rip anyone to shreds! And that's why he's been getting all these scars, why he has to spend days after the moon in the hospital wing—because he's attacking himself instead!"

"Bloody hell," murmured James. "And he never gets dressed in front of us…." He shook his head. "No, this is crazy. He can't be a werewolf; he just can't." Everything James had ever heard about werewolves—that they ate children, and kept their nails filed into claws—clashed completely with the bookish, wry Remus, who often looked too weak to even lift a finger. But maybe that was one of the effects of lycanthropy, a sickness that waxed and waned with the moon….

"James," said Sirius, cutting through his thoughts. "When was the last time Remus disappeared?"

James blinked. "It was…it was the night we got Peeves to follow Snivellus around the school with his cymbals. You and me got detention for a week after, which I remember ended the day we had Quidditch tryouts, so…September twenty-third?"

"Okay, September twenty-third." Sirius went over to his bed and dug around underneath it until he found the astronomical event chart Sinistra had given them at the beginning of the year. "Look: September twenty-third was the day of the last full moon."

James snatched the chart from Sirius, his hands shaking. He was right—Remus's last disappearance had also been on a full moon night. One time might have been a coincidence, but twice in a row?

"Merlin." James put a hand over his mouth. "Our roommate is actually a werewolf."

In absolutely any other situation, Sirius would be going on endlessly about proving James wrong—but now he was silent, looking as peaky as Remus often did. Remus Lupin, a werewolf.

James lowered himself onto the edge of his bed, his knees feeling like they were about to give out. Peter collapsed by the window and froze there as if he'd been Petrified.

"So," James said eventually, breaking the silence, "what're we going to do now?"

"Well, we have to tell him we know," said Sirius.

"Why didn't he tell us?" Peter squeaked. "I wish I knew before now that we've been living with a werewolf."

"He probably thought we'd be scared of him," Sirius muttered. "Or tell everyone and get him kicked out of school."

"Of course we won't," James said firmly. "Whatever he is, he's our mate. And it's not his fault he's a werewolf."

"Of course not," Sirius agreed.

"But werewolves…they work with You-Know-Who, don't they?" Peter said tentatively. "Greyback and the others…they eat the children of anyone the Death Eaters don't like."

James snorted. "There's no way Remus is working with the Death Eaters, Peter. Think of who you're talking about here. Re's the one who sent us all furry mouse socks for Christmas."

"I know," said Peter defensively. "I just meant…what if he gets angry once he realizes we know about him?"

"Remus doesn't get angry about anything," Sirius pointed out. "When we tell him, and he realizes that we don't care and we still want to be his mates, I think he'll actually be the opposite."

"We do still want to be his mates, right, Peter?" James asked, looking at Peter pointedly.

"Of course," Peter insisted.

"Then it's settled." James gripped one of his bedposts, still stunned by what they'd figured out but more certain than ever that he wanted nothing to change between him and his friends, Remus included. "As soon as Re returns from the hospital wing, we tell him."

Sirius nodded, leaning back against the wall. "Well, it doesn't look like any of us are going back to the Astronomy Tower tonight," he observed.