Joan has never noticed this cafe before. Perhaps due to its lack of advertising, she thinks, but the idea disappoints her a little -- she thought she knew all the little places near the brownstone. Sherlock often insists that she should memorize their surroundings, every second if possible, because you never know what can help you solve a case. He tells her that he could walk the block blindfolded, knowing exactly where he is the entire time. Whether or not this is true, and she suspects it is, she tells him not to do it. Cars are rather unpredictable.

And at the moment Sherlock is being insufferable, so she's stepped out to catch her breath. He's been at the wall for hours now, attempting to collate data that they just don't have enough of. He probably didn't sleep last night and she didn't get much either, so she went out for coffee and a breather. She needs a bit of space to process.

And because she can't remember ever seeing this coffee shop before, she steps in.