"… Mycroft?"

The voice at the top of the stairs was small, unsure and almost nervous. Mycroft almost flinched. His brother was never nervous, never unsure, and definitely never small. Every movement Sherlock made was grand and bold and—

"Mycroft?" Broken. Broken beyond repair.

"Sherlock." Mycroft steeled himself and glanced upwards. His younger – much younger, too young – brother stood half-hanging over the bannister, his feet only barely touching the carpet below. His hair was wild and as messy as a bird's nest, obviously he had avoided the customary brush before bed. Again. The older Holmes almost smiled. His lips twitched, anyhow, and Sherlock's light eyes widened in response.

"I…" Mycroft faltered, and Sherlock visibly slumped. This was the opposite of good. "I have to go. University, Sherlock. That's why I took all those exams."

"University is far away." It wasn't a question. Sherlock was clever – too clever – for his age. He knew. Of course he did.

"Yes." He answered anyway.

Mycroft watched as his brother's face screwed up, pain, confusion, sadness flitting across his face one by one. He settled on an emotion Mycroft was familiar with. Anger. Sherlock was always angry with the world and everything in it.

" Everyone's so stupid! Except you and me, Mycroft. We're clever."

The older brother felt the same, but he'd learnt to hide it. "You're going without me."

Again, not a question, but Mycroft felt obliged to reply. "Yes," A pause, a sigh. "I'm sorry."

"Sorry." Sherlock rolled the word around his mouth and spat it out. Sorry? Mycroft's lips tightened. Sorry. For leaving him with mother and father. Sorry. For going when he promised he'd never leave.

"Pinkie promise, Mycroft! You can't break it, or I'll… never talk to you again!"

The younger Holmes slid from the bannister and stepped warily down the stairs, considering Mycroft as if he was a strange new animal who might bite if he got too close. It hurt. "Take me with you."

"I'm sorry," Another pause, another sigh. "I can't."

Silence. Sorry. And then:

"Please."

Sherlock's fists were clenched tightly, but that didn't hide the tell-tale shine in his eyes and the wobble in his lip. It took all of Mycroft's self-restraint not to fall to his knees and gather his brother in his arms and stay like that for as long as he was needed. But he couldn't. Caring is not an advantage. Who had told him that? Their father? So instead he shook his head and distractedly smoothed a hand down his suit lapels. "Be good."

"No." Sherlock tripped down the last two steps and scrambled to Mycroft's side, "No. I won't be good. You have to stay. You can't—"

"Be good," Mycroft repeated in a firm voice. Be brave. "I'll write to you. Every week."

"No."

"Sherlock…"

"No."

So Mycroft touched the top of his brother's head briefly, carefully – he was like china, so fragile – and drew away. He'll be fine. He wouldn't.

Mummy will look after him; he'll be fine. She would, but he wouldn't. In later years Mycroft would blame himself for Sherlock's addiction. If he hadn't left at that moment, or maybe if he'd said something else…

He felt Sherlock's eyes on his back as he walked away. His figure would be blurred by the unshed tears in his brother's eyes, but he was watching all the same. Watching him leave.

I'm sorry.