Fresh out of college, Xu Anran and her two roommates, Jiang Yu and Liu Yiyi, find a ground-floor apartment in a prime location with an impossibly low rent. An elderly neighbor and Anran’s own mother warn them the place is wrong, but financial pressure forces them to sign. Buried in the contract is a clause that waives the landlord’s liability.
Soon after moving in, strange odors drift through the rooms, and dark red stains seep from the walls. Anran digs into the building’s history and finds that years ago, when the complex was still called “Happy Home,” a wife was murdered here. The suspect was acquitted because the body was never found. The agent refuses to return their deposit, citing the contract. Jiang Yu and Liu Yiyi, both struggling with jobs and savings, refuse to move out. The three agree on one rule: never leave anyone home alone.
When Anran returns alone to grab her laptop, she discovers a hidden iron door under her bed leading to a hand-dug basement. Their newly adopted puppy runs inside and barks frantically at a wall rigged with a high-tech vibration monitor. The basement’s industrial exhaust fan was purchased the day after the murder. Objects start moving on their own, and Liu Yiyi secretly lets her boyfriend stay over.
They find old blueprints revealing another half of the basement sealed behind a partition wall. After Jiang Yu is laid off, she blames the apartment’s feng shui, and in a fit of rage, smashes the wall open with a hammer.
Inside is a woman’s body, preserved with embalming treatments.
The original landlord—the suspect from the old case—rushes over. He confesses: his wife died of a sudden heart attack. He couldn’t bear to let her go, so he sealed her body inside the wall and installed monitors to track any movement in the wall.
Anran calls the police immediately. After the body and the case are processed, the three pack their bags overnight and move to a more expensive but safer place.
