When he moves into a worn-down apartment, his neighbor leaves him with one horrifying rule: never turn on the light, or he’ll die. Each time the switch clicks, a scream bursts from the wall. Then one month later, the neighbor is found hanged, and a scheduled text names the newcomer as the killer. To clear himself, he follows the trail back to a pair of twins and a hidden family secret. The final truth is even darker—he has an identical brother, and the man under suspicion only began a chain of events the other one finished. The detective knows it all, but he still can’t prove a thing.