The case was over, at least in Sherlock's mind, for about two days now. He was certain that the killer would be found in one of the abandoned flats, and it was no surprise when, after a brief chase, the unfortunate murderer was pinned down and handcuffed by one of the more able police officers. Even Lestrade began celebrating earlier - he had arrived to the scene smelling of lager, with a spring in his step and the weekend on his mind. John was there, too, breathing heavily from the brief scuffle with the killer when he bumped into him while they were sweeping the desolate building. Yes, Sherlock thought, their presence was redundant at best, but it was a better way to spend the evening than to watch John prepare for his date and then leave with a small smile on his lips, only to return in the early hours of the morning.
It had been about a month since Dr. Watson moved in to 221B Baker Street, and Sherlock had been pacing himself. He felt the unmistakable stab of attraction to the doctor during their first public meal, and his mind was made up when he learned that the good doctor did not hesitate to shoot the cabbie when Sherlock's life was in danger. Sherlock's mind quickly tagged John as "safe," and after a couple of weeks "warm," and, after some internal struggle, "exciting." Despite these pleasant revelations, Sherlock chose to proceed with caution, and enjoy, for the time being, only John's friendly companionship. It did not, however, deter him from gently nudging John in the right direction by compromising the doctor's dating life.
And so that evening, when John was putting on his good shoes and chatting absent-mindedly about "Kelly," Sherlock informed him that the police had a strong lead about the whereabouts of their latest suspect, and John stopped, sighed, and cancelled the date with a single text. If Sherlock had allowed himself to make a conjecture on the subject of John's reaction, he might have said that the doctor felt guiltily relieved. It was, however, a guess, and he carefully discarded it. Only three hours later they were standing in front of the handcuffed killer and Sherlock felt a mild twinge of panic at the thought that it was still only 10 pm and it was very possible that "Kelly" liked John enough to allow him come by for a nightcap. Luckily for Sherlock, John looked entirely pleased with how the evening turned out so far, if Sherlock could judge by the way he grinned at the approaching Lestrade.
"Got 'im, boys," Lestrade said, looking at Sherlock and then John, "Thanks for stopping by, even though, I do admit, I did not expect you to come…"
Sherlock opened his mouth to say something, but noticed that Lestrade was already priming himself to inflict a rather painful companionable slap on Sherlock's back. Taking a swift step away, Sherlock avoided Lestrade's assault, leveling him with a restraining look. Lestrade did not take offense, but turned to John and delivered a resounding, profound slap on John's back, making the doctor stumble slightly forward and even cough a bit.
"Blimey, Greg," John quickly regained his balance and turned to the DI with wide eyes, "I think it's time you went back to the pub."
"Sorry, John," Lestrade answered, but the doctor was already smiling with a crinkle in his eye and Sherlock allowed himself a brief smirk, before noticing the way John moved his shoulder, as if he wished for his clothing to rub against his stinging back.
"Right, I think it's time we all headed home," Sherlock said, and left John to say hasty goodbyes while he hailed a cab. As always, he was rather successful, and soon they were riding home in companionable silence.
John was silent in the cab, and Sherlock allowed himself to observe the doctor from the corner of his eye. John was moving slightly, imperceptibly, pushing against the seat as if to entrap the warm residue of Lestrade's hand; Sherlock noticed that, and the absent-minded way John played with the phone in his hands, and the way he finally hummed and turned it on.
"I might as well check if Kelly is still up for a late night cup of coffee," John explained, and in the brief moment when the doctor's eyes were lit up by the screen of his phone, Sherlock saw that John's pupils were dilated.
Kelly was not, in fact, up for a late night cup of coffee. When they made it to the flat, John quickly excused himself and made his way to his bedroom, while Sherlock lay on the couch and pondered the night's events. Granted it had been only a month since he met Dr. Watson, but he was accustomed to learning everything of value about the people who surrounded him in the matter of hours, or, at most, days; John seemed to be set on surprising him, even though the doctor did not do it intentionally. Take, for example, that night's incident with Lestrade: there was a brief moment of physical contact with the doctor and the detective, and as a consequence John's mind reverted to the thoughts of physical pleasure (hence his imperceptible movements in the car, and his attempt to get in touch with Kelly); Sherlock was certain that John was not attracted to Lestrade - there were no accidental touches or lingering looks, and John had made it clear to the whole of Scotland Yard, and to Lestrade personally, that he was not interested in men.
That, of course, left Sherlock with the impossible deduction that John enjoyed pain. And yet, judging by the women John chose for himself, it was also clear that pain had not been introduced into John's sexual life. Again, Sherlock felt that it was hasty to assume that John, who had a rich sexual history, was not aware of his own tastes in the bedroom. And yet, Sherlock's only bid on John's future reciprocation rested on the possibility that when it came to sex, John could have overlooked a few major facts about himself. It was a flimsy hypothesis, but it was one nevertheless, and further experimentation would be needed for it to be proven wrong or true.