Residents at Gangsan Mansion live their days in fear when the girl in unit 202 is found dead and no clues are found for the serial killing that occurs in a 10-day interval. Meanwhile, the neighbors start to become suspicious of the man in unit 102, who has bought the same suitcase as the one used in the murder, orders pizza every time there’s a murder, and gets absurdly high water bill. The murderer also becomes aware of their suspicion, and the last battle to protect the next victim begins…