Regulus has never seen his brother's face so cold.

"Why?" he asks, and it barely stirs the musty air in the hallway around them, barely makes it across the space between them—too much space, always growing, stretching on and on to the point that Regulus has lost all hope of crossing it. "Why, Sirius?"

Sirius's expression is all but unreadable, cast in shadows and flickers of firelight from the candles on the walls. He shakes his head, as if Regulus is the unreasonable one, as if Regulus is the one doing something impossibly brash and reckless. There's a knapsack tossed over one shoulder, and his hand is fisted, white-knuckled, around the worn strap. If it's shaking, if Sirius is wavering at all, Regulus can't see it.

Fourteen years he's loved his brother, but he's never understood him.

"Damn it, Reggie," Sirius rasps, and his voice is thick with something—tears or anger or frustration or hate, maybe all of them knotted up and brimming inside him, ready to burst out as…this. This final act of rebellion from which there will be no return. "Just…move."

Regulus is fourteen and small for his age, fourteen and a Slytherin and more likely to be found tucked away in the library than roughhousing the way most boys his age do, but nevertheless he plants his feet and refuses to so much as waver. "No," he says stubbornly. "I won't. Sirius, don't do this. Mother and Father—"

Three quick steps bring Sirius right up in front of him, and Regulus flinches back before he can stop himself, more used to his brother's dismissive shoves and frustrated swats than anything else—that's all he's really known since Sirius's Sorting, and it's only gotten worse since his own. There's a pause, a hesitation, and then a hand on the collar of his robe, shockingly gentle. Regulus stays tense, but opens his eyes to glance up at his brother through his lashes. The expression on Sirius's face is grim, sad, resigned, and the guttering candlelight isn't quite enough to hide the bruise blossoming like a garish flower across one aristocratic cheekbone.

"Mother and Father," Sirius repeats, almost mocking, "are the ones who gave you those." His fingers ghost over the four matching bands of color just hidden by Regulus's robes, crossing the backs of his shoulders and marching down his bicep.

Regulus bites his lip, wants to say I deserved it, I should have done better, but…doesn't. Because he knows that he did well, did better than any of his classmates on Slughorn's test, and though he isn't anywhere near brave enough to say that to their parents the way Sirius doubtless would, he had wanted to. The words had strained in his throat, trying to escape, even as his mother brought the cane down on his skin.

They still want to come out, and Sirius at least won't care, but Regulus still locks them away deep inside himself. Once he starts speaking those kinds of things, he won't ever be able to stop.

And then Sirius says, soft and almost breathless, "Come with me."

Regulus looks up into grey eyes so like his own, and all the coldness has fallen away, replaced with something that looks like—

Like hope.

His shoulders sting. He takes a breath, another, and this time when Sirius lifts a hand towards his face he doesn't flinch.

"I'm a Slytherin," he says, just as quietly, as though Sirius is going to forget.

And Sirius smiles, crooked and sad but still just faintly warm, and it's enough.

"Yeah," he agrees, and the words are light but the expression on his face makes his tone a lie. "But you're my brother, too."