The Slytherin common room is quiet, the green lamps casting soft light over cold stone. It is past midnight, and everyone else is asleep, leaving the room in a silence that feels heavier than usual.

Regulus sits curled in the corner of the couch by the fire, head resting on the armrest, a book slipped from his hand as sleep claims him. His breathing is calm, his dark hair falling into his eyes, making him look almost peaceful.

You watch him from the staircase, biting your lip. You have noticed it for weeks now, the way he never rolls up his sleeves, the way he pulls his arm away if anyone’s hand comes close. The way his eyes harden for a split second if someone even jokes about it.

No one else seems to see it. But you do.

And tonight, curiosity outweighs caution.

You step closer, the carpet muffling your footsteps. The fire crackles, the only sound in the common room as you kneel beside him, carefully reaching toward his arm where the sleeve is bunched slightly, revealing a pale sliver of skin.

Your hand trembles as you lift the fabric, just enough to see it.

Your breath catches.

The Dark Mark is there, dark against his skin, the skull and serpent winding around his forearm like something alive. You feel cold all over, your stomach twisting as you let the sleeve fall back, heart pounding in your ears.

Regulus stirs, his eyes blinking open, confusion flashing across his face before he follows your gaze. His body goes rigid, and his hand flies to pull the sleeve down, his breath catching as he realizes what you have seen.

“I—” His voice breaks, a sharp sound in the quiet. “You shouldn’t have—“