It would be grossly inaccurate to say Sherlock never forgot anything, even if one discounted those bits of information he found dull and unimportant and therefore deleted with extreme prejudice. Two, or perhaps it was three now, millennia was a very long time and it was inevitable that some things would slip from his head without his leave or notice. It would be accurate, however, to say that Sherlock never forgot anything he deemed interesting. It was entirely unsurprising, then, that when Mike Stamford walked in with someone in tow, not only did Sherlock know who he was (Army doctor, invalided home – either Afghanistan or Iraq, psychosomatic limp), Smaug remembered exactly who he had been (Come from under the hill, and under the hills and over the hills his paths led. And through the air. He that walks unseen. The clue-finder, the web-cutter, the stinging fly. Chosen for the lucky number. He that buries his friends alive and drowns them and draws them alive again from the water. Come from the end of bag, but no bag went over him. Friend of bears and the guest of eagles. Ring-winner and Luckwearer and Barrel-rider. Bilbo Baggins. Little thief).
(Observation: The man's face is identical to that of the hobbit Bilbo Baggins – odds, incalculably y small. Observation: Beneath stronger scents of tea and wool and gun oil, the man smells of pipe-weed – Southfarthing Leaf. Conclusion: Man is reincarnation of Bilbo Baggins. Data: Reincarnation is real. Query: How does it work?) Finally, Mike had done something useful.
"Mike, can I borrow your phone? There's no signal on mine," Sherlock asked, not because he felt any urgent need to get back to Lestrade, but because he needed to get Bilbo's attention and see his reaction. Will he remember Sherlock? Smaug? Does he even remember his own past self?
Sherlock watched Bilbo closely during his ensuing exchange with Mike (Phone clearly in trouser pocket. Theory: Mike has incorrectly remembered the phone's location. Alternative theory: A subconscious instinct to not give belongs to a dragon is overriding common politeness. Alternative theory: A conscious instinct to not give belongings to Sherlock is overriding common politeness. Conclusion: Insufficient data), but was still surprised when a mobile was suddenly being held out to him. "Er, here. Use mine."
"Oh. Thank you," Sherlock said, surprised into offering wholly unnecessary courtesies to an almost stranger. (Note: Do not let Mycroft know about this reaction.) But what is a thief doing randomly offering his possessions to a dragon? (Theory: Bilbo does not recognize/remember Smaug. Conclusion: Bilbo offers his things to random strangers. Theory:?)
"It's an old friend of mine, John Watson," Mike told Sherlock as he crossed the room to take the proffered phone. Sherlock filed away the information that a reincarnation does not necessarily have the same name as the previous one – just as well, the name Bilbo Baggins would have stuck out like a sore thumb in 21st century London – before taking the phone from Bil- John and beginning to type his message.
"Afghanistan or Iraq?" Sherlock asked. He needed more data.
"Sorry?"
"Which was it – Afghanistan or Iraq?" Sherlock said again, for once too excited about the whole potential wealth of information in front of him to mind the repetition.
"Afghanistan," John replied. He kept talking, but Sherlock ignored it, uninterested in the inevitable reaction to being deduced – confusion, suspicion, anger, or some combination thereof. Instead Sherlock returned John's phone, having both solved Lestrade's case and gleaned all the information he could about John off it, shooed off Molly, who'd come back with his coffee, with some offhand comments about her lips, and pretend to work on his computer while figuring out how to keep an eye on this mystery Mike had brought to him.
(Data: He mentioned to Mike he was looking for flatmate this morning. Data: John was an old friend Mike hadn't seen in a while. Data: Mike had brought John to see Sherlock, a man of no particular importance in his life. Conclusion: He and John were meant to be flatmates.) Of course. Mike was in sparkling form today.
"How do you feel about the violin?" That was a human thing, Sherlock thought. Knowing about people before committing to a close association, like being flatmates.
"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," said Sherlock, wondering if John was always this slow. Bilbo had been slow, but that had been in Rivendell, after he'd gotten old and dull. The little thief had been quick, though, quicker than Smaug even. Of course, that had been back when Smaug's brain had been bigger and slower and too full of gemgoldmetal-firebloodrevenge to think at all, so perhaps he couldn't hold John to those standards.
"Oh, you ... you told him about me?" John asked Mike. As though Sherlock needed to be told something so obvious.
"Not a word." Mike replied.
"Then who said anything about flatmates?" said John
"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." Really, Sherlock was tired of these inanities. He'd give John a day to get his thoughts together, then he might be a little less slow. Besides, Sherlock needed to get his riding crop back before Molly touched it, and he needed to prepare him Mind Palace for all the new information about reincarnations he was going to be adding.
"How did you know about Afghanistan?"
"Got my eye on a nice little place in central London. Together we ought to be able to afford it." Sherlock said, pulling on his coat and scarf and ignoring John's question entirely. "We'll meet there tomorrow evening; seven o'clock. Sorry – gotta dash. I think I left my riding crop in the mortuary."
"Is that it?" John said.
"Is that what?"
John gave him a look like it was Sherlock, and not the reincarnation of a thief of a hobbit, who was the odd one in this situation. "We've only just met and we're gonna go and look at a flat?"
"Problem?" It seemed perfectly straight-forward to Sherlock.
"We don't know a thing about each other; I don't know where we're meeting; I don't even know your name." Ah, not enough data. Sherlock could respect that, but he really didn't have time for it now.
Sherlock gave him once last look up and down, but he had already seen everything he needed to. "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?" Because that was a hobbit thing; there weren't keen on adventure unless you dropped them right in the middle of it before they realized they'd begun.
"The name's Sherlock Holmes and the address is 221B Baker Street." He did that that smile and wink thing that seemed to make him more likable. Just to be on the safe side. "Afternoon."
This was going to be interesting.