An ironclad rule has been passed down in the old district: once the lights go out, don't open your eyes, don't look back, and don't answer anyone. Chen Mo, a former criminal investigator who runs a late-night bookstore, can see shadows at the end of the hallway that shouldn't exist whenever the streetlights go out. Delivery driver A Zhao attracts followers by livestreaming "the three minutes after the lights go out," until her camera captures a man in a gray robe, Shen Deng, smiling at a photo of her younger brother. Forced to team up and investigate the blackouts, the two discover that every time a light goes out, a living person is "replaced." The lamplighter, Tao Jiunye, security guard Zhou Dawu, pursued by shadows, and the boy Xiaoman, who always appears before an incident, all gradually push Chen Mo toward the truth: he himself is the only person who was never replaced in that first blackout.
