[It's definitely not new to John that when Sherlock is investigating, he goes wherever he feels the need to with no real regard for whether or not he really can or anything like it. And if someone comes in he has this ridiculous ability of getting them to leave no matter why they're there. Most often, it goes pretty quickly too.

John often apologises for it because Sherlock doesn't go about it in nice ways. This time, he ends up staring at the closed door and it only takes a few moments for Sherlock to tell him to follow her and see if she knows something.

That doesn't usually happen, but Sherlock doesn't give him a chance to question it. So he follows this (beautiful) complete stranger to figure out if she knows something about a murder. Because that is what people want to talk about, Sherlock. Jesus Christ.]