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When Sherlock returned home, he was greeted by the sight of John Watson sitting in a chair at the top of the steps. He had a nine-millimeter handgun in one hand, and in the other a bottle of clear liquid. The grimness of his expression, and also the gun, caused Sherlock to stop short on the top step and take stock of the details. "Watson," he asked evenly, "you do realize we have several perfectly good locks, don't you?"
"Sherlock." John nodded, almost imperceptibly. "I need to talk to you."
"I assure you that any conversation we may need to have can be conducted far more comfortably inside, where there is proper furniture and lighting." He paused. "Also, there is no need for weaponry."
"Isn't there?" Watson asked, though he did relax his grip slightly where the gun rested against his thigh. He leaned forward slightly. "See, Sherlock, I've been doing a bit of deducing of my own lately."
"I'm thrilled for you," Sherlock said. "I am to presume from my reception that I have been the object of your deductions?"
John nodded again, stiffly.
Sherlock leaned against the banister, arms folded. "Go on, then. What have you deduced about me?"
"You don't eat, Sherlock," John said bluntly. "Not only when you're working—you don't eat ever, unless Lestrade or someone has you on the spot."
"What brought you to that conclusion, then?" Sherlock asked. "After all, you're hardly in my presence every hour of the day."
"I do the shop," John said, a little chidingly. "It doesn't take a consulting detective to notice that when I buy food enough for two, only half of it gets eaten. There hasn't been anything in the kitchen but severed heads for the past week and you've noticed nothing."
"I could be eating out," Sherlock proposed. "Or take-away."
"If you were ordering take-away, there would be evidence in the bin or on the draining board, both of which I also take care of while you're lost in the throes of genius," John said. "And if you were leaving the flat often enough to be getting two thousand calories a day, Mrs. Hudson would've said something by now."
"You put tremendous faith on Mrs. Hudson's omniscience," Sherlock said quietly.
John's reserve finally cracked. "Jesus Christ, Sherlock, you don't even drink water! You swan about in that stupid coat and scarf ten months out of the year, you talk until you ought to be hoarse, you run halfway across London—I may not be a genius, but I am a doctor. Don't insult me."
"Fine," Sherlock said after a slight pause, and a small smile began to play across his lips. "I don't drink...water. What else has inspired you to such melodrama tonight?"
"You don't sleep, either," John said warily, and his grip on the pistol tightened again. "You might lay on the couch and shut your eyes, but you never go into REM. I asked Mrs. Hudson to stop changing your sheets for you and they gathered dust."
"So, don't eat, don't sleep..." Sherlock counted these off on his fingers. "I suppose you're next going to accuse me of not breathing?"
"After that stunt you pulled on the Thames Barrier last week, I wouldn't doubt it," John said sharply. "But I was actually going to point out that in the months of our acquaintance, you've been in perfect health."
"A capital offense, I know," Sherlock said.
"No sniffles," John said relentlessly. "No coughs or flus. No insect bites, no shaving nicks. You've never turned an ankle or skinned a knee or even gotten bruised, whether we've been crawling through storm drains or fighting with professional assassins."
"I'm resilient," Sherlock said diffidently, pretending to study his nails.
John's frown deepened. "You've fought a professional assassin and survived, Sherlock, and unlike me you've had no formal training in hand-to-hand."
"No formal training," Sherlock said, but he looked up sharply from under his fringe.
"And during that kidnapping case, the little Polish girl, you threw a fifty-five gallon drum of water off a roof. Lifted it clean off the ground. While it was full." John let go of the bottle long enough to wave his phone at Sherlock. "If I've got the maths right, you beat the Olympic record for your weight class with that one."
"You are a soldier as well as a doctor, John," Sherlock said. "You're well aware of what a man can do under the influence of adrenaline."
For some reason, that made John laugh, or at least sort of snort in a way that could be taken as laughter. "A man. Right."
"Have I said something funny?" Sherlock asked.
John leaned forward, staring intently now. "What is that thing you say, Sherlock?" he asked, low and urgent. "That after you eliminate everything that's impossible--?"
"Then whatever remains, however so improbable, must be true," Sherlock said. "I believe you suggested I put that on a T-shirt and sell it from my web site."
John ignored this; he was fingering the gun again. "A man can't go without eating for weeks," he said, as calmly as if he were reading off phone numbers. "A man can't go without sleep for days at a time. A man can't lift three times his weight over his head without breaking a sweat. A man can't jump from a fourth-floor window and hit the ground running. So what does that make you, Sherlock?"
Silence reigned, pregnant with possibilities. It burst under the clatter of Sherlock's laugh. "No, no—don't stop, John," he said, straightening. "Not when you're just getting to the good bit, you can't stop there."
"What more is there to say?" John asked stiffly.
"You tell me," Sherlock said, spreading his hands a moment before folding his arms again tightly. "For instance, I suppose you've considered that I don't burn up in direct sunlight?"
"Considering how often we have a clear day in London, I'd say the evidence is inconclusive," John said.
"I do have a reflection, though, surely you've noted that," Sherlock said. He had begun to pace frenetically about the landing, each turn taking at most two strides. "I have no particular opinion of crosses."
"Anything visible to the naked eye will reflect in a mirror, that's physics," John shot back. "And for you to care about crosses, you'd have to have a bit more faith and a bit less ego."
"I don't care for garlic at all, though, there is that." Sherlock stopped and turned to John, still smiling slightly. "And you've failed to address the most obvious point."
"I've been talking to Molly at Bart's," John said, raising his chin slightly to look Sherlock more squarely in the eye. "She told me exactly what you 'borrow' from the morgue. And what you don't bring back."
The smile all but vanished. "I have my experiments," Sherlock said, suddenly tense. "Stains, coagulation, spatters--"
"Not in this quantity," John said. "And never where I can see them. I don't mean to complain, Sherlock, but when have you ever bothered to hid your little experiments from me before?
Sherlock began to pace again, and his laughter this time was brittle. "Well played, Dr. Watson, well played indeed," he said. "A marvelous piece of deductive work, and you know what that means, coming from me. And thus you meet me here, armed and prepared—is that holy water?"
"Whiskey," John admitted.
Sherlock huffed once, and resumed his train of thought. "You meet me here, prepared for heroics—though when have you ever required liquid supplements to your courage?--you meet me here and tell me that you know everything, you've found me out—what exactly did you expect me to do about it?"
"I wasn't certain," John said, and for the first time he averted his eyes.
"No, no, no," Sherlock pronounced firmly, punctuating each word with sharp gesture. "Unacceptable answer, John. You know me too well for that, have obviously spent a great deal of time thinking about these matters. And you may not have noticed it, but you aren't the only one who's been doing a bit of deducting about his roommate."
John went very, very still. "What do you mean?"
"Is it my turn to detail my observations?" Sherlock asked. "Let's start with the gloves, then—you are careful to don gloves whenever you're with a patient, even for the most cursory examinations, but you frequently study corpses bare-handed. Conclusion: it is not your own health you're worried about.
"Or what about the metal? You avoid handling it, you know—unless you already know the composition, like coins or doorknobs. You even avoid Sarah when she's wearing certain necklaces, and the only jewelry you've given her has been ten-carat gold even though sterling silver would be less of an insult to your much-maligned bank account.
"And if you're going to analyze my health history, Doctor, consider your own—you are frequently ill with a vague constellation of symptoms, at least once a month but never on the same day of the month. You seem to bring these illnesses back with you from travels, because you do always travel for a day or two—never the same place, but always somewhere in the countryside, which only partially explains the smells and stains left on your clothes when you return. These trips are urgent enough to take you away from any other business, even the Polish girl's kidnapping, and yet you never speak of them after you return."
John stood up, still clutching the gun in his right hand. "Are you finished?" he asked tightly, and clenched his jaw on the end of the sentence.
"Hardly," Sherlock shot back. "A former soldier should be comfortable with a certain degree of casual nudity, yet you wear bath robes and dressing gowns and don't even roll up the sleeves of your jumper when you're sweating—there is something on your body you want to hide. You keep a fastidiously clean room and use only unscented toiletries and detergents, which together suggest that you are unusually sensitive to olfactory inputs. You prefer dogs to cats, but dogs dislike you nearly as much as they dislike me. You can comment on the phase of the moon off the top of your head, but unlike me you do not make a deliberate study of the lunar calendar."
"Are you done now?" John asked, barely opening his mouth so the words came out in a growl.
That made Sherlock smile again, a dangerous little smirk. His teeth were very, very white. "Not quite. Because you've deduced exactly what I am, John, so you must realize that that gun is of laughably little use to you. You've remained remarkably calm and coherent while you laid out your evidence, which suggests that you came to this conclusion a while ago, and had time to work through your emotional reactions, time to plan.. So why choose tonight of all nights to confront me? Why face me defenseless, if you truly think I'm dangerous?" He leaned forward, very close to John's face. "Unless, of course, you're not actually defenseless at all."
John inhaled deeply, nostrils flaring. "What's that supposed to mean?" he asked.
Sherlock made a show of checking his watch; when he looked up, something deep in his eyes glinted red. "It means it's less than four minutes until the full moon rises. And I think we've both had enough deduction for tonight. So, my friend...what happens next?"
Very carefully, John set the handgun down.