Disclaimer: Rowling and Moffat and Gattis and Thompson and Doyle.
A/N: A brief note before you read this chapter. I reference two "theories of truth" in a conversation between Sherlock and Remus. If you've taken philosophy, you may recognize the terms. If not, a brief explanation: the correspondence theory of truth says that whatever explanation fits with all of your observations is the one that's true, while the coherence theory of truth says that whatever explanation fits with your preconceived notions about the way the world works is the one that's true. Thought you might like to know.
Sherlock had gotten bored again. This time, Remus was mostly bemused. Then again, this time Sherlock was mostly acting amusing, rather than spending days staring at the wall. It was hard, when Sherlock came into the flat carrying a bloody harpoon, not to be reminded of all the various ridiculous disguises, props, and messes that had alternately hidden the Marauders in plain view and made them stand out when they least wanted to be noticed. Despite the distraction of the unbidden, fond memory, however, it wasn't hard for Remus to bite down his nostalgia and react to Sherlock as John Watson would. Remus had grown up since his days with the Marauders, and he knew very well by now how to be an adult.
Accordingly, Remus disapproved vaguely as Sherlock explained that he'd taken the Tube because none of the cabs would give him a lift. Then it was the cigarettes again—Remus would really have thought that someone as fiercely independent as Sherlock would hate chemical dependency, but there it was. Remus refused to give in to Sherlock's pleading. It wasn't the first time he'd been up against stubbornness, after all. Even so, he wasn't sure if he could have lasted all day had it not been for the—
"Single ring," Remus noted.
"Maximum pressure just under the half second," Sherlock agreed.
"Client."
The client had an unusual case, which was good considering Sherlock's intense boredom. Remus wasn't quite as relieved as he usually was to get a strange case, though, because this one was rather . . . canine. He'd managed for a year and a half now to keep his lycanthropy a secret from his eminently observant flatmate, but there had been far too much luck involved in the success for Remus's taste, and it looked like the luck might just be running out.
The first clue that this case was outside of even Sherlock's usual purview came when the client was describing the scene of the—well, not quite the scene of the crime, because it wasn't clear that there had been a crime, but the scene of the event. "There's a place—it's . . . it's a sort of local landmark called Dewer's Hollow. That's an ancient name for the devil."
Sherlock raised his eyebrow and said, "So?"
Remus, on the other hand, had learned from Dumbledore that sometimes things that seemed ancient and superstitious were actually real and useful. A huge dog with glowing red eyes sounded like something Hagrid might keep around, and it made all the sense in the (wizarding) world for an unpleasant magical creature to show up in a place with an archaic, mysterious connection with forces of evil. Henry seemed to be a Muggle, though, so this logic wasn't worth explaining to him. Remus tried to get at the issue in a more Muggle-friendly way, asking, "Did you see the devil that night?"
"Yes," Henry whispered. "It was huge—coal-black fur, with red eyes. It got him, tore at him, tore him apart. I can't remember anything else. They found me the next morning, just wandering on the moor. My dad's body was never found."
Remus had heard of werewolves whose fur was black when they transformed. As for the red eyes—Henry could have imagined those, or they could have been a trick of the light, or they could have been the result of some spell or other. Werewolves were certainly known to kill, but it was suspicious that Henry's father's body was never found. Of course, some werewolves searched the areas where they transformed after they returned to their human bodies, in order to clean up after themselves, so Henry's father could have been buried by a werewolf. On the other hand, suppose he hadn't actually died, but rather turned into a werewolf and left of his own accord in order to protect Henry? Remus had heard of such things happening.
Remus tried to tamp down his werewolfy thoughts, reminding himself that there were many possible explanations for Henry's story. "Hmm," he said aloud, filling a silence that had already stretched on too long. "Red eyes, coal black fur, enormous . . . dog?" He had to say it: "Wolf?"
Sherlock shot him a glance, and Remus got a sudden feeling that there would be conversations later. For now, though, Sherlock was on a case, so he looked back at Henry and suggested, "Or a genetic experiment."
The case broke Sherlock's boredom (luckily for Tube riders across London), and it distracted him from following up on that glance he'd thrown in Remus's direction during their interrogation of Henry, at least for a while. Remus expected Sherlock to corner him at some point during a lull in the investigation, but then Sherlock made a blunder that forced him to avoid antagonizing Remus for a few days: he denied having friends.
Remus had been on the receiving end of enough insults in his life to have developed quite a thick skin, but he had started letting down his defenses around Sherlock in a way that he hadn't done since he'd been with the other Marauders. With them, that trust had only formed after they had discovered that he was a werewolf, but somehow Remus had become comfortable with Sherlock without any lycanthropy-related conversations. Sherlock's acceptance—however grudging, however backhanded, however rude—was something he'd come to depend on, and even Remus's steady nature didn't stop him from leaving Sherlock at the fireplace and wandering into the night, at least for a few minutes.
After that little fiasco, Sherlock had felt the need to apologize and win Remus back, and Remus figured that this was the only reason that the trip to Dartmoor concluded without a shoved-up-against-the-wall interrogation. Overall, Remus was quite happy with the case: the mysterious hound wasn't a werewolf or a magical beast after all, so Remus didn't have to feel guilty about hiding information from his Muggle client.
Sherlock was quiet all the way back to London. Even for someone as fond of silence as Remus, it got to be unnerving, and the context made Mrs. Hudson's welcome back even more jarring than it usually was.
"Oh, boys, how was it?" the landlady crooned as soon as Sherlock threw open the door and the crime-solving duo stepped inside. "Did you solve the case, Sherlock?"
"Yes, Mrs. Hudson, and now I have another mystery on my hands, this time involving John, so I'd prefer you to leave us alone and find some way to busy yourself for the next few hours. Surely you're capable of that."
"Sherlock, I lived here twenty years without tenants and I—" Mrs. Hudson broke off because Sherlock had made it up the stairs and slammed the door in the time it took her to screech this at him. Remus, who was halfway up the stairs at this point, turned around and glanced at Mrs. Hudson, who mouthed, "Domestic?" Remus shook his head.
Given that Sherlock had slammed the door, Remus had to open it in order to get into the flat. He briefly considered not entering, even turning around and leaving, since Sherlock had let his temper get the best of him and it would serve him right to learn that slamming the door was a bad idea when you wanted someone to follow you. Then Remus took a deep breath and opened the door, because he knew enough about himself by now to realize that he was stalling, and that he wouldn't be doing himself any favors by delaying a conversation that was inevitable by this point.
Well—it was inevitable unless Remus Confuded Sherlock. With his hand still on the doorknob, Remus considered the option, but he knew that he wouldn't be able to live with himself if the charm had any side effects on Sherlock's amazing mental capabilities. Remus shut the door behind him and sat in his usual chair.
"Until this case, John, I had regarded your 'about once a month' anxiety episodes as lycanthrophobia," Sherlock said as soon as Remus was seated.
"That's not a word." It wasn't. Remus had checked, repeatedly. Whether he wanted to name the fear of people like himself, or the intolerance, there wasn't a word for it. Now, if he were a butterfly, people who feared him would be called mottephobes, and if he were foreign, people who refused to tolerate him would be called xenophobes, but, since he was a werewolf, there wasn't a word for people who found him frightening or intolerable.
Sherlock, meanwhile, charged ahead. "Well, then it should be. As I was saying, I thought you were a lycanthrophobe. But you were able to deal with the idea of a hellish canine running wild on the moor at night rather well, don't you think? Too well for someone with a pathological fear of hellish canines that roam the moor at night."
"It wasn't the full moon!" Remus protested.
"And you noticed. You noticed. Most people wouldn't, but you keep track of the full moon because . . ." Sherlock put his hands to his temples and muttered to himself, "Once you've eliminated the impossible, whatever remains, however improbable, must be true."
Remus leaned back in his chair and stretched his legs out in front of him, trying not to let on just how nervous he was for the conversation he was about to allow to occur. "Where your logic takes you is going to depend on your definition of 'impossible.'"
Sherlock leapt off of the sofa and began pacing. "I go by the correspondence theory of truth, John—surely you've notice that."
"Everybody follows the coherence theory to some degree," Remus retorted.
"I don't. I don't give a damn about the rules. You know that; you've played Cluedo with me. If the only possible explanation of all the facts is that the victim did it, then the victim did it and that's the truth. The truth doesn't get to be impossible."
Remus stood too, glad that he trembled with boredom rather than nervousness. It meant that he wasn't shaking now. "Well then. Deduce away."
"You retire to your room for a few days every month at the full moon. You refuse to let anyone see you during these few days. You keep track of the lunar cycle in your head. Your tone of voice changed when you suggested to Henry that his father had been killed by a wolf, but it wasn't your scared voice. I know what that sounds like; if I'd forgotten, I would have had an excellent reminder when I locked you in the lab. So you're acutely aware of lunar cycles, but you don't have a greater-than-usual aversion to abnormal canines that roam at night. Either your phobia is very targeted, or . . .
"It seems that the other explanation of the facts is impossible, but you said that what I discovered would depend on my definition of impossible. Targeted phobias are not all that uncommon, although I would not have expected to find one in a person as seasoned as you. A targeted phobia is the more plausible explanation of the facts, however, so your hint about the definition of impossible suggests that I should look elsewhere.
"Very well. The other explanation of all the facts is that you are a werewolf."
Remus looked at Sherlock, expecting some sort of statement about how ludicrous this notion was, or else an avid interrogation on the finer points of lycanthropy. Neither occurred. For a minute, the two men stared at each other. Then Sherlock snapped impatiently, "Well? You've got to tell me how I did!"
"You're right," Remus said simply, letting his arms rise slightly from his sides and then fall back into place as he shrugged.
Sherlock narrowed his eyes, fingers twitching. "I posited two potential explanations. Which one is right?"
"The second one."
Sherlock was stunned into silence for a minute before saying, "There is, of course, the possibility that you're lying, and that you were lying when you referred to my definition of impossibility, and that you simply have a very targeted phobia of werewolves, or indeed of the full moon, although then I need to find a motive for you lying to me, and . . ."
Rarely had Remus been so scared of an impulse he felt while in his human form, but then his impulses were rarely so intense. His right hand was fully steady as he pulled his wand from where he had been keeping it recently, inside the forearm of his left sleeve. Pointing the wand at a book on the coffee table, Remus said, "Wingardium Leviosa." The book floated to eye level and bobbed in the air.
"The H.O.U.N.D. drug must still be in my system," Sherlock muttered, rubbing his eyes with the pads of his fingers.
Remus let the book drop back to the table, but he kept his wand in his hand. It had been a very long time since he had used it, and its weight was somehow steadying. The grip still felt familiar, more than a gun's ever would. This was Remus Lupin's weapon of choice. "As you like," he said to Sherlock.
"Fear and stimulus, fear and stimulus, fear and—BUT THIS ISN'T FEAR!" Sherlock had been pacing, but now he whirled on Remus. "The H.O.U.N.D. drug works on fear and stimulus. Once you're afraid, it can make you see things you wouldn't normally see, especially if a slight stimulus is placed in front of you. But I wasn't afraid when you pulled out that stick and pointed it at the book; I was just confused. I don't scare easily. And there shouldn't have been any stimulus in that direction, either; nothing's moving. But if the drug isn't what's making me see things, then what—"
Remus wound his fingers tightly around his wand and said quietly, "I'm a wizard."