Hongyu accused of familicide, is in hiding. His twin, Guan, a nyctophobic, is an ace detective. They want the police file on the familicide, to prove Hongyu innocent. Guan probes a multiple murders case, and Hongyu replaces him at nights.
Zhige diverts the police on a wild goose chase and reaches the police station in search of Gaun and the familicide file. Liu is taken hostage. A deeper, sinister plot is suspected.
The police analyst surmises, with logic, that this serial killer's first kill has not been unearthed yet. That first kill can give vital clues about the serial killer. So, the police start digging again and find a 5-year-old murder.
The Jiangzhou police draw a black about Hu's burglary 2 years ago. Hongyu and Shutong visit the burgled home. The owner, Dong Qian, is a professor. He later disappears, leading to a search. Guan shakes off Captain Zhou after a long chase.
Hongyu outmaneuvers the killer. Police arrives and Guan is considered the victim. Guan puts in a recommendation for rookie cop Zhao Qian, who had been secretly ordered to tail him.
Guan had put away Qi in prison for gang related crimes. Upon release, Qi spots Houngyu, the twin, quarrels with him and is knocked down. Later, he is knifed and murdered. Guan worries because DNA under Qi's fingernails may match Hongyu's.
Houngyu ventures out in the day and finds that Yaoji deals in drugs. This tip helps Guan nail Yaoji and his boys. The police are puzzled how Guan knew about the drug dealing. Qi's murderer is still at large, although Ah Man is suspected.
Guan gets a lead from Houngyu to Yaoji's drug stash. He suspects if Houngyu was into drugs earlier. Liu takes Zhou to the scene of the familicide, which Houngyu is accused of. There, they discover a dual murder in a car parked outside.
A double murder of a celebrity and a girl creates a stir. There is a furor when the press discovers that Guan is still with the police and Guan now has 1 week to solve the case. Sensing a serial killer's work, outside police join in.