Sherlock had spent the day trying to distract himself. By lunch, he had managed to solve three separate police inquiries and it had got to the point where he was trawling through some of the more mundane cases on his blog, a task he hated and delayed doing for as long as possible. He didn't want to admit it, but it was the Doctor's fault. Sherlock was not accustomed to becoming too attached to people: the incident with Redbeard had shown him that love was a weakness rather than a virtue. Yet despite his best intentions, he had become attached to the Doctor, who did not judge him or call him a freak as most people did not. Much as he disapproved of sentiment, he admired the Doctor's ability to care so deeply and grudgingly admitted that this was one of his greatest strengths. Whatever the Doctor said about his memories being the only things that would be lost in the genetic transformation, Sherlock was resolved. The man who would soon walk through the door of his lab was not the Doctor, although he might wear his face, but a cheap copy. Sherlock would tolerate him, but never fully accept him.

It was late in the afternoon when they finally arrived. Sherlock was in the labs testing some samples from the scene of a particularly vicious murder when Mike Stamford and "John Watson" walked through the door. Mike was one of Mycroft's associates who had the task of keeping an eye on the latest crop of budding doctors for any who might be suited to the challenges of working for one of the intelligence agencies: UNIT folk law maintained that Martha Jones had been spotted by Stamford as a likely candidate for intelligence work long before that whole incident with the Judoon. From a quick glance, Sherlock could see that Mike was upset about the role he was playing in the Doctor's disappearance. His bloodshot eyes suggested several sleepless nights and his appearance was more dishevelled than usual. After a quick glance at his guests, Sherlock continued to study them whilst apparently occupied by his Petri dish. The false memories appeared to have taken hold of the Doctor, who showed no signs of recognising Sherlock and who had abandoned his usual easy gait for the ramrod straight posture of a soldier. He walked with a limp, evidently psychosomatic, which came as a surprise to Sherlock: the Doctor's notes hadn't said anything about signs of mental trauma. Maybe it was a subconscious reaction to whatever had led the Doctor to this rash decision in the first place? Sherlock filed the information away as something to investigate later. No doubt his new flat mate would have some explanation from his imagined life that could offer some interesting clues as to the limp's real origin.

As the Doctor (Sherlock couldn't yet bring himself to think of him as John) and Mike made some banal observations about Bart's recent improvements, Sherlock felt it was time to join the conversation. As it so happened, he wanted to text Lestrade the solution to one of the investigations he had solved that morning to serve as a little reminder that he was free to work on the mysterious spate of serial suicides plaguing London, which sounded vastly more interesting than the usual simple cases Lestrade bothered him with. The London criminal classes apparently had no imagination.

"Mike, can I borrow your phone? There's no signal on mine."

"And what's wrong with the landline?"

"I prefer to text."

"Sorry. It's in my coat."

"Here. Use mine."

Sherlock was surprised. The character of John Watson created by the Doctor was not the type to just loan a random stranger his phone. Maybe the Doctor had exaggerated the extent to which he would lose his memory? Trying to hide his sudden interest, Sherlock quickly replied, "Thank you."

An awkward silence ensued which Mike quickly decided to break by introducing his companion, "This is an old friend of mine, John Watson."

Without bothering to introduce himself, Sherlock reached over to take "John"'s phone and started to text. The obvious way to test how many of the false memories had stuck was to apparently deduce key facts about "John"'s past and see his response. The natural point to start was his supposed military career. Perhaps Sherlock might even be able to find out more about that limp, which was bothering him.

"Afghanistan or Iraq?"

The Doctor frowned and looked over at Sherlock as though asking for an explanation. Sherlock ignored him and continued to type.

"Sorry?"

Sighing, Sherlock again asked "Which was it – Afghanistan or Iraq?"

He briefly dared to look over at "John". Usually this was the point where ordinary people would start to swear at him or call him a freak. Instead of showing any negative reaction, the Doctor just seemed confused and intrigued as to how Sherlock had known.

"Afghanistan. Sorry, how did you know?"

Molly walked into the room with his mug of coffee before Sherlock could respond. Slightly irritated at the interruption, he brusquely thanked her while making some small talk about her lipstick. As she left the room, she seemed a little upset. In retrospect, maybe he shouldn't have pointed out how small her mouth was. The Doctor always used to try to stop him when he went too far with his deductions… Sherlock quickly suppressed the memory and returned to the matter at hand, his new flatmate.

"How do you feel about the violin?"

"I'm sorry, what?"

"I play the violin when I'm thinking. Sometimes I don't talk for days on end. Would that bother you? Potential flatmates should know the worst about each other."

"John" turned to Mike for an explanation. Sherlock realised too late that he had no yet broached the subject of a flatshare. He was far too used to the Doctor keeping up with his deductions that explaining his rapid thought process seemed unnatural. The joys of ordinary people. "Oh, you ... you told him about me?"

"Not a word."

"Then who said anything about flatmates?"

The Doctor seemed intrigued rather than repelled by the idea of living with Sherlock, the high-functioning sociopath. So the Doctor hasn't lost his taste for danger then, mused Sherlock. He will always be addicted to a certain lifestyle. Perhaps this flatshare will be better than I anticipated…

Picking up his greatcoat, Sherlock started heading for the door: no need to prolong the encounter longer than necessary. "I did. Told Mike this morning that I must be a difficult man to find a flatmate for. Now here he is just after lunch with an old friend, clearly just home from military service in Afghanistan. Wasn't that difficult a leap."

"How did you know about Afghanistan?"

Sherlock ignored the question. Might as well see if he can figure out how I knew. "I've got my eye on a nice little place in central London. Together we ought to be able to afford it. We'll meet there tomorrow evening; seven o'clock. Sorry – got to dash. I think I left my riding crop in the mortuary."

Just before he went through the door, "John" stopped him. "Is that it?"

Reluctantly turning back, Sherlock replied "Is that what?"

"We've only just met and we're going to go and look at a flat?"

"Problem?"

"We don't know a thing about each other; I don't know where we're meeting; I don't even know your name."

He doesn't even know my name. Sherlock had not anticipated how hard this was going to be. Ignoring the wellspring of negative emotions welling up inside of him, he resorted to his usual failsafe when in any particularly difficult or overwhelming situation. He started to deduce the man in front of him. John Watson, that is, not the Doctor. Looking over the man in front of him, there was no trace of the timelord he had once been proud to call his friend.

"I know you're an Army doctor and you've been invalided home from Afghanistan. I know you've got a brother who's worried about you but you won't go to him for help because you don't approve of him – possibly because he's an alcoholic; more likely because he recently walked out on his wife. And I know that your therapist thinks your limp's psychosomatic – quite correctly, I'm afraid. That's enough to be going on with, don't you think?"

As he went through the familiar rhythm of deducing a person's innermost secrets, Sherlock reached a decision. The Doctor, for whatever reason, had chosen to become someone else. He would never get his friend back. But that was no reason to not give John Watson a chance. This man with the same face and the same addiction to a certain lifestyle. Sherlock owed that at least to the Doctor.

As he walked out the door, Sherlock called back to John, "The name's Sherlock Holmes and the address is 221B Baker Street. Afternoon."