You found an empty compartment three cars down, slipping past clusters of chattering students, past a group of first-years pressed against the window with wide eyes, past a pair of redheaded twins who barely glance up from whatever they're whispering about — huddled together like conspirators plotting the fall of civilization itself.

The compartment door slides shut behind you with a satisfying click. For now, silence.

Outside, the countryside rolls past in swaths of green and grey, dotted with sheep and stone walls. Rain taps lazily against the glass.

Then footsteps. Heavy, confident, unhurried. Someone walking past your compartment — then stopping. The silhouette of a tall figure framed against the frosted glass.

A knock. Sharp. Twice.