Molly and Sherlock form a short-lived, crime-solving partnership in "The Empty Hearse."
Louise: They do.
Jace: Why do these two keep coming back to each other?
Louise: Well, I sort of... I know why, why- Molly simply simply loves him. And it's not a sort of... I don't think it's a stupid thing. I think, there's something pure and beautiful about her love for him, and so… He, Sherlock, has become... You know, we've seen more of his vulnerabilities, and humanity, and I think Molly saw it from the start, and I think that that's one of the reasons why she cares for him.
And in terms of him with her, I think she surprised him. I dunno, I really like that these tiny moments happen and other stuff’s obviously going on behind, you know, that we don't see, as an audience. And something about those tiny moments tell you that -- this sounds odd, so you might have to winkle out exactly what I'm on about -- but it's like those tiny, tiny moments make you feel like there's something else happening somewhere else. Does that make sense?