A drabble written in response to this photo set on Tumblr.
Changing himself, stepping into the role of another had been so much easier than Sherlock had expected. If he tried hard enough, he could almost believe that he was who he said he was.
"Sherlock?" A whisper of his name, a voice so familiar despite so long without, it took all his willpower not to turn, not to react or acknowledge the person calling out to him. John shouldn't have been there; he should have been safe in London and far far away from Sherlock.
"Sherlock?!" The voice was louder, nearer, and Sherlock couldn't miss the hope and pain.
A hard grip on his arm spun his around, and Sherlock was greeted by John's drawn and haggard face; he somehow looked so much older than Sherlock remembered the last time he'd seen him over two years ago. The surveillance photos were just not the same. "Puis-je vous aider, monsieur?" Sherlock asked in flawless French, struggling to keep his turbulent emotions from showing on his face. As dead as Moriarty may have been, the game he had set in motion was far from over. Sherlock was doing his best to dismantle it, but it was far too soon for him to be revealed; there were too many pieces still in play, too much risk at hand. It wasn't safe for John, for any of them yet.
For a long moment, John stared, taking in his familiar features, and the unfamiliar: the brown eyes, the straight blond hair, the suit far different than anything Sherlock would have worn. And for one horrifying moment Sherlock thought he'd been caught, while desperately wishing that John would realize, and that he could stop pretending. Just as abruptly John let go, stepping back as the spark faded from his eyes as he seemed to fold into himself. "Sorry, so sorry. Thought you were someone else."
As John turned and walked away, his shoulders slumped and his head lowered, Sherlock could almost pretend that he didn't already miss his touch, that seeing John's hope, only to shatter it with his calm denial didn't destroy him inside. Almost.
French translation from Google Translate: May I help you, sir?