You steady your wand with both hands and force more power into the seal, channeling every ounce of focus through the trembling wood and stone. The charm lands like a hammer strike, and the trapdoor flashes silver before the glow is swallowed by a violent surge from below. The chamber lurches as though a giant hand has gripped the foundations of Hogwarts, and even Snape staggers back a step. Your scar burns with such heat that tears sting your eyes, but you hold the spell anyway, refusing to let the door break.

For one breath, the pressure below eases, then returns with a deeper, more terrible force that makes the candles burst into blue sparks. The book on the table springs open by itself, pages whipping wildly as if some hidden command has been answered. Snape turns sharply toward you, his expression thin with urgency, and mutters that the seal will not hold unless the ritual is reversed at the source. The hidden passage is still trying to open, and now you know the next choice must be made in the seconds before it tears free.