Joan, Sherlock and others in “Unfinished Business”

Joan

Well, it certainly sounds like you had feelings for her.

Sherlock

Perhaps but... nothing so mundane as love. I was adrift back then. I had-had no purpose. My so-called peers made me feel that that might always be the case. Abigail, she gave me a gift. A view inside a mind capable of murder.

Watson

So she was your first...

Sherlock

Killer, yeah. Without intending to, she-she helped me understand who I was and-and what I might do with my life.