When Sarah moved into her new apartment, the landlord warned her never to open the locked door at the end of the hallway.“It’s sealed for a reason,” he said, handing her the keys—except one, which was missing. At night, Sarah often heard faint scratching behind that door. Sometimes a whisper—like someone calling her name. The sound grew louder each night, as if whatever was inside was desperate to be heard. One stormy evening, lightning knocked out the power. Alone in the dark, Sarah lit a ca...