Two men stood in front of the mantelpiece of 221B. The first picked up the pocket watch that had lain there, largely unnoticed, unconsidered, for months. "You recognized this, from the Chameleon Arch. Do you understand what it means?"
After a moment, the second man nodded. "He's not what he seems."
"He's a Time Lord. And he has no idea. Whatever brought him here, whatever he's hiding from, he's in incredible danger. So much danger that he put away everything that he was, gave up everything god only knows how long ago, to wind up here with you. And now someone's got a bounty on Time Lords, and they're looking for him. Which means that you're in danger now as well."
"What do I do?"
"Watch him. He's an extraordinary human being. Who he really is, though... who knows? It may begin to bleed through. You may see changes in his behavior. He may become more reckless. I don't know who or what he was before, but recklessness and arrogance are generally hallmark traits of my kind." There was a shadow of a smile on his face. "As long as his disguise holds, and he will be safe. Well. Safer. I'll try to find out what he's hiding from, and who's sending rogue Time Agents after him. I'll let you know what I find out."
"Is there anything else?"
"Just one thing: whatever else you do, Sherlock, do not let John Watson open this watch. His true self will emerge, and whoever is looking for him will be able to track him. Keep him safe. You'll hear from me soon."
The two men locked eyes for a long moment, then Sherlock nodded. He took the watch from the Doctor and tucked it away in his pocket.