Seriously? Sherlock resisted the urge to groan aloud. What it must be like to exist in such a dull mind that never comprehended the evidence around him. He restrained himself to a roll of his eyes that John couldn't see and a press of the phone a little closer to his ear.

"Then don't."

Sherlock made his voice easy and smug, a well established actor of his own right, exactly as he would sound if he had just managed to get one over on John.

"Do use your mind, John, I'm not in Southwark. Why would I be in Southwark? Nasty streets and boring cafes, I just needed to make sure you were out of the way long enough for me to conduct an experiment at home. You would have thought too loudly, it would have distracted me."

Don't come up, just walk away. But not suspicious, not so that Moriarty would have his subordinates kill him.