"Sherlock!" Mycroft slams his fist down on the table angrily. "Can't you be more mature?"
"No. How's the diet going, by the way, Mycroft? Don't answer that - I already know."
Ever since he'd been a teenager, Sherlock had known how to push Mycroft's buttons. It was like second nature for him, pissing his brother off. Of course, Mycroft wasn't really angry. Irritated, yes, but Sherlock could count the times Mycroft had been angry at him on his fingers.
The first time Sherlock had seen his brother's full fury had been when he was fourteen and Mycroft had been twenty. He'd came home from Uni for Christmas break, and the first thing he had found was Sherlock, high out of his mind.
"Sherlock, I'm home," Mycroft had called, walking along the hall towards his younger brother's room. Perhaps Sherlock had matured, he had hoped.
He received no response after knocking, something he'd learned the hard way it was now necessary to do. But Sherlock always responds when he doesn't want Mycroft to intrude on him - and he's not responding now. Mycroft frowns and tries the door handle - locked. Maybe Sherlock is sleeping, but he doubts it. It takes him all of two seconds to pick the lock, and only then because he's not paying attention completely. He has other things on his mind - college work doesn't concern him, it's easy, but the impending Syberian nuclear crisis does.
Every thought slips from his mind as his eyes find his little brother curled up in a chair, a needle appearing to have just fallen from his hand. Glancing around the room, it was painfully obvious that Sherlock had been... experimenting. The boy appeared to be coming down from his high - all the better, Mycroft grimaced. Could Mummy not control the boy? Or had she simply given up trying?
Mycroft used the few minutes he knew he had before Sherlock woke up to clean up the room, carefully disposing of all evidence. He couldn't live with himself if Sherlock was caught - and he knew the boy would be, he was careless like that. Just as Mycroft returned to the room, Sherlock started to stir. Perfect timing.
"Mummy?" Sherlock groaned, sitting up, not turning to immediately look towards the intruder.
"You wish." Mycroft hadn't meant for his voice to sound so dark, but it came out that way - it fit the situation, though, and he didn't bother correcting it. Mycroft swore he'd never seen Sherlock sit up that fast before. The boy scanned the room desperately, and when he realized it'd been cleaned and Mycroft without a doubt knew, he sat back down with a thud, childishly refusing to meet his older brother's eyes.
"Sherlock."
"Go away."
"No."
The conversation had turned into a three hour shouting match, and ended with Mycroft slamming Sherlock violently into the wall.
"I won't let you ruin your life if it's the last thing I do! Sherlock, you have no idea! You pride yourself so much on your brain - these drugs will kill it, Sher."
Yes. Yes. There it was. A small crack in Sherlock. He'd pry it open, force sense into the boy.
"Sherlock - everything you want right now, you won't have any of it. You get caught once, and you're screwed, Sher. You'll ruin the rest of your life. You get that marked on your record - forget a job, forget everything, Sher. That's all people will see. No one will see the Sherlock I see. The genius inside."
And Sherlock's crying, and Mycroft doesn't know why, but he holds his little brother close to him, and promises that it'll all be okay, that he'll make it all okay.
Mycroft will always make it better.