Sherlock POV
Sherlock doesn't sleep after John leaves at four in the morning. Instead he sits in the chair organizing all that has happened since he came back. He doesn't notice a woman has entered the apartment until she clears her throat.
"Hm?" He looks up.
"Hello Sherlock." The woman says. He narrows his eyes.
"Do I know you? I feel like I know you. Maybe I do. But sometimes I delete unimportant people to make space for more important information. Are you here for a case? Please say you are. But make it interesting. I don't do boring cases." Sherlock goes on and stands up to walk over and look out the window.
"I'm not here for a case, not really." The woman says.
"Boring. Next!" He yells out but the woman doesn't leave. He looks her over, up and down, but nothing particular stands out.
"You don't look like my brother's usual messengers but who knows, even my brother can be surprising sometimes." Sherlock says going to the kitchen to pick up the now cold tea sitting on the table.
"My name is Mary."
"Boring."
"I think it's actually quite lovely."
"Well you're delusional." Sherlock replies.
"I doubt it. I'm here about John." Mary says and Sherlock stops in his tracks slowly turning towards her.
"John." He says slowly.
"Yes, John. You know the man that believed you were dead when in fact you weren't. The man that shed tears for you. The man that went through a lot of pain because of you. That John." Mary says pointedly.
"Oh, I thought you were talking about the other one." Sherlock waves his hands dismissively but really he wants to know exactly what this woman wants. He looks back at her and comes close to her. He first sniffs her hair and then looks at her coat.
"You're the pregnant wife." Sherlock says.
"Girlfriend, though I'd like to say wife. I must admit, it took you a while to figure out who I was." Mary smiles cheekily.
"Well I don't have time for trivia." Sherlock dismisses her again.
"Sherlock. John told me you were scattered but not to this extent. I am here about John. Aren't you the least bit curious?" Mary says.
"I don't get curious. I know things." Sherlock replies though in fact he is curious as to why she is here at Baker Street without John.
"I came to say that when the day comes, whether it's tomorrow or in years, I want you to promise me that you will take care of him." Mary says and Sherlock frowns.
"Of whom?" he asks and Mary just rolls her eyes.
"Of John." she replies.
"Why would I need to take care of him? He's a perfectly capable grown man. Though not always observant I would say he can manage in the world. He's managed until now." Sherlock says and looks to the wall where a case he dropped lures him back in.
"Because he is your friend. Because I know how much he means to you and how much you mean to him. Because you win. John may not know it, you may not know it, and maybe in this case I'm the most observant one. But I know when I've been defeated. And I only want John to be happy, so you win. But only when John decides it. And only if you promise me that you will take care of him." Mary says her eyes looking dangerous. There's something about her that Sherlock can't quite pinpoint and it's frankly quite annoying because he hates not knowing.
"What do I win?" Sherlock asks.
"Seriously? That's what you got from that? Just promise you will take care of him." Mary asks. Sherlock, unsure as to what is going on, just nods. He knows he doesn't have to promise that in order to actually do it and he has a feeling Mary knows that. Before he can say anything else Mary leaves the apartment and Sherlock is left alone again, to ponder John, his girlfriend, and the fact that he desperately needs a case.