Disclaimer: I own my own ideas and words, but not the concept, premise upon which this story is based, or the characters therein. They belong to the BBC and Sir Arthur Conan Doyle.
A/N: Because I just rewatched A Study In Pink and couldn't resist trying my hand at Sherlock's train of thought. I hope I did all right. I tried to keep him as close to character as possible, while still retaining the bond between Sherlock and Watson, which is important to both and in many ways very much against the character of Sherlock Holmes. Hope this works out, and there may be more if inspiration strikes. I've been bouncing around fandoms lately, though, so it might be a while before my muse comes back around to this one.
Despite John's use of his own words against him, Sherlock Holmes was most profoundly not an idiot.
He was brilliant, a genius, without any of those annoying emotional reactions to get in the way. He felt a vague sort of affection for Mrs. Hudson, a bit of glee at taunting Anderson and Donovan, and something like friendship and fascination for Dr. John Watson, no matter that he'd only met him the day before.
No wonder, since the man had surprised him more than anyone else had in years. He'd been surprised that John reacted with amazement to his deductions rather than the annoyance and hostility it usually invoked (not that he cared, of course, but it did tend to make things more difficult when the police were unreasonably suspicious). He'd been surprised when John had defended him (unnecessarily and incorrectly) against the drugs bust. He'd been surprised when John had tried to get to know him, albeit awkwardly, by asking about his romantic life. He'd been surprised when John had reacted without censure but with calm correction when he'd made an apparent social error in assuming that a stillborn child would not affect a parent fourteen years later.
Surprised or not, however, Sherlock still had the power to put two and two together and get four.
Which is how, while explaining to John how exactly one could tell a good Chinese restaurant from the bottom third of the door handle, he concluded that John Watson had very nearly died in Afghanistan from a bullet that almost ripped through his heart.
Fact: John himself had admitted that he had nearly died, as evidenced by his quiet comment about not having to imagine what his last thought would be.
Fact: John had also confirmed his suspicions (based on the way John had handled his cane without difficulty on the right side and the location of his intermittent tremor) that he had been shot in the shoulder. Specifically, the left shoulder.
Consider: the damage necessary to render a man as valuable in his skills as John Watson so injured as to be invalided home from an area of the world where his skills were very much in demand would have had to have been extremely severe. A shot to the shoulder would likely mean shattered bone at the very least. The sort of weapons used by insurgents in Afghanistan would likely have sent the bullet most of the way through his body, if not all the way through. A shot to the left shoulder would have risked damage not only to a lung but also to his heart.
Conclusion: John Watson had been injured in combat by a bullet that tore through his chest, probably from behind, and narrowly missed his heart (if it had hit his heart, John would not still be alive). Conceivably, it might have punctured a lung. Based on John's morals (as evidenced by his waiting to shoot until Sherlock was in imminent danger) and his convictions (as evidenced by his quiet acceptance of the necessity of killing one man to protect another), it was unlikely that he had been shot in the back due to cowardice or an attempt to flee. More likely, he had been utilizing his medical skills and was paying less than usual attention to his own safety. It was also likely that that patient had sustained a leg injury, possibly a severing of the femoral artery or a shattered hip, which had resulted in the development of the psychosomatic limp.
It took him only seconds to perform this sequence of thoughts, during which time he was simultaneously explaining a different train of deductions to John and deciding the best way to go about slipping the surveillance that his brother would most certainly be assigning to him after this incident. It was a relatively unimportant thought in the grand scheme of things, since obviously John had not died and therefore it was enough to note the weakness in his left arm for future reference and dismiss the thought from his mind, the same way that he dismissed and forgot all details that were unrelated to his work as a consulting detective.
For some reason, however, the knowledge took up residence in his carefully ordered thoughts. It planted itself straight in the middle of his mental filing system, on top of a cabinet, so to speak, and refused to be properly filed or thrown out.
That's not to say it was an all consuming idea, or that he couldn't ignore it at will as he did everything else. Sherlock did, however, find it interesting that he was unable to control this thought, that it seemed determined to remain as a reminder that John Watson had very nearly not come into his life.
That had a slight sobering effect to it, since he was already developing a mental file of the things John did which made him less than boring to work with. Chief among them at the moment was the fact that he had been willing to kill to save Sherlock's life.
John Watson should have been dull, a soldier who conformed to a rigid (and frankly slightly ridiculous) command structure that trained individuality out of its members, without the sheer intelligence to keep up with Sherlock and with an unfortunate tendency towards emotional reactions. That he wasn't dull merited further study, which as his flatmate, Sherlock would have sufficient opportunity to conduct.
Yes, John Watson had surprised him.
That surprised him most of all.