Sherlock buries his head in his arms. He can barely hear the voices of Mycroft and Lestrade coming from the other side of the closed door, but he can't make out their words. He doesn't need to. His brother is threatening Lestrade, obviously, and there's no way the man will be able to stand up to him. Nobody can. Mycroft is like a force of nature that way, sweeping resistance aside and leaving compliance in his wake.
A broken moan reaches Sherlock's ears and to his horror he realises it is his own. He hears it again and this time he doesn't care. His moans come faster and louder until they become great gasping vocalisations of pain. He doesn't want to do this. He doesn't want to be locked away for his safety. If Mycroft would just go away.
The door opens and Sherlock swallows his groans. This is it, his last moments of freedom, even if they are miserable and pointless.
Mycroft stops just inside the door, waiting, hoping for Sherlock to spit his customary 'piss off' in his direction, but his brother doesn't. He wants to go to him, scoop him up in a hug and comfort him, but that's not something the brothers do. Not for the first time, he wishes they did. All he can do is watch as this relative stranger approaches his brother and begins to talk.
Greg crouches down by the sofa, his voice gentle. "Sherlock." The young man doesn't uncover his head or acknowledge that he has spoken. "Come on, son, I need you to look at me. Mycroft's said you can stay with me a few days if that's what you want, but you need to tell us if it is. Come on, that's it." He breathes a sigh of relief as the kid uncurls and sits up.
The black feeling lightens momentarily to grey and Sherlock can breathe easier. He tries to say that, yes, of course he wants to stay here, but he can't get the words out despite the air flowing easier through his lungs. His hands fly to his hair and he tugs on it. If he can just focus on something besides his ridiculous emotions, he'll be able to talk, he knows it.
Greg's heart aches seeing his young friend in so much pain and he grabs Sherlock's wrists. "Hey, now, Sherlock. None of that. All we need is one word. Yes or no."
Sherlock calms, feeling Lestrade's firm grip on his wrists. It's something concrete that anchors him. He manages to whisper, "Yes."
He's amazed when Greg smiles at him and tells him, "Right. There's that decided then."
From by the door, Mycroft nods to Lestrade. The other man has promised to be there for Sherlock and to phone if things get worse. It's a risk and they both know it. If things go pear shaped, it's Mycroft's brother who will pay the price. Still, sending Sherlock away would probably kill his brother at this point and Mycroft knows he's ill equipped to be of help. It's painful, but he makes himself take his leave. "Sherlock... be well," He finishes lamely and steps out the door.
Suddenly, Greg is terrified. He understands exactly what he's got himself into. If he fails Sherlock... He gives himself a shake and belatedly realises he's still holding the kid's wrists. He lets them go and is distressed when Sherlock's hand shoots directly to his hair once again and begin tugging. He needs to find a distraction for him.
Sherlock barely registers when Lestrade stands and walks away. The greyness is getting darker. He lets his hands fall to his lap, surrendering for the moment. The next thing he knows, a small cube is being placed in his hand. It's approximately 2.25" on a side with 9 coloured squares on each side. The colours don't appear to be in any coherent order.
Greg points at the cube. "If you need something to do with your hands, fix that. Don't rip your hair out by the roots." He knows it's not much of a distraction, but it works with his daughter. He'll have to find something else to use on a longer term basis.
Quietly, almost so softly Lestrade can't hear it, Sherlock asks, "What is it?"
Greg actually laughs. This kid is a genius and he's never seen a Rubik's Cube. He explains what it is. "It's a puzzle. You've got to rearrange the squares so each side is a solid colour."
Sherlock processes that for a moment and he looks at the piece of plastic in his hands. Automatically, he starts to calculate the number of possible combinations and has to retreat to his Mind Palace to do it. He soon arrives at the number 43,252,003,274,489,856,000. It would be daunting, but he can already see that a few simple repeated moves of the cube are all that is needed. Sherlock solves the puzzle within 4 minutes and tosses it towards Lestrade. Amazingly, his mind feels a bit clearer. He doesn't feel good, but he's not falling apart anymore.
Lestrade catches the cube and gawps at it."I've been trying to solve this bloody thing since '83 and you do it in 5 minutes."
"Less than 4," Sherlock corrects. "I could do it faster now."
"Right, right." Greg is still staring at the cube. "Bloody hell."