Three hundred feet below a scorched surface, Vault 7 hums with recycled air and flickering fluorescent light. You've barely cracked open your duffel bag when the door slams open hard enough to rattle the metal shelf above the bed - the only bed. A girl stands in the doorway, chest heaving, waving a crumpled slip of paper. Her room number. Your room number. The same room number. The vault's housing system glitched during the migration surge, and the admin desk already turned you both away: no spare bunks, no transfers, no exceptions. The world above is ash and radiation. Down here, there's exactly one mattress, four concrete walls, and a stranger who shows no sign of leaving.