They're playing Operation again. It's kind of ironic, given the subject of their conversation.
"Bone marrow transplant. Do they think it's going to work?"
Mycroft shrugs, then proceeds to extract the wish bone. "Hopefully."
"Need a donor?" Sherlock asks as he removes the broken heart.
"Would you do that for me?"
"Of course, brother dear. Your turn."
xxx
They have agreed not to tell their parents. Mummy will probably guess there's something going on, but she can't know for sure.
When his brother is gone he puts on his coat and wanders into the night. He doesn't want to worry Mrs Hudson, and yet he needs someone to talk to. He briefly considers showing up at John's place; but he knows that Mary will be there too, and that's enough to make him change his mind.
Lestrade also has a family, so that leaves only one person he can turn to.
It's not fair of him to bother Molly after the recent breakup with her former fiancé, but the burden in his chest is so heavy he doesn't really have a choice.
She gives him the resigned look he knows so well when she finally opens the door.
"It's really late, Sherlock," she starts, only to trail off as soon as she catches a glimpse of his face. "What's wrong?"
"It's about my brother, he's – very ill."
"Come in," she says, and he does.
xxx
"I take it that you had a pleasant evening?"
Of course his brother would notice that he smells different this morning; he's talked to Molly for the better part of the night, and they've ended up falling asleep curled up together on her sofa.
"I didn't sleep with her, if that's what you're hinting at," he states plainly, as the anaesthesia is starting to take effect.
"Technically you did – sleep in the same spot, to be more precise."
"Shut up, Mycroft," he mumbles, right before the drugs finally knock him out.
xxx
"We're compatible," he informs Molly as he's perched on the edge of her bed. "The doctors are going to start the treatment as soon as feasibly possible."
"That's good news," she mutters, and it's apparent she's struggling to keep her eyes open. "What about we get some sleep now?"
A quick glance at the clock tells him it's way past midnight. "Okay," he shrugs, then lies down beside her.
He listens to each soft breath she takes until he eventually falls asleep.
xxx
Mummy rings him, begs him to tell her the truth about Mycroft's health conditions.
"He's just a bit under the weather. He'll be fine."
Her stifled sob is clear indication that she's seen right through his lie, but she doesn't say anything.
John gives him a questioning look from the other end of the room; he simply turns on his heels and darts through the door.
xxx
Mycroft is quite pale, his hand is shaking as he picks up the tweezers and starts playing.
"The doctors say I'm reacting well to the treatment. I will be out of here soon."
The buzzer sounds as he attempts to remove the butterflies in stomach. Sherlock shakes his head and hands him back the tweezers.
"Try again," he says, and this time his brother successfully remove it.
xxx
Their parents are only too happy to hear that their eldest son is now recovering nicely. The four of them have dinner at his brother's place; that reminds Sherlock of the early days of his childhood – when he and Mycroft still talked to each other, and enjoyed it quite a bit too.
Mummy embraces each of them in turn before leaving, he lets her because he knows that's exactly what she needs.
Later on the two brothers play Operation again, and this time Mycroft wins.
xxx
A couple of days later he's knocking at Molly's door, carrying a bag of Chinese takeaway as a means to gain entrance to her flat.
"I brought dinner," he states simply, and she accepts it as the 'thank you' it's meant to be.
They spend the rest of the night watching telly, and he falls asleep with his head on her lap.