Kan Yiu-yeung, Ku Ka-keung, Kiu Po-po and Kiu Tai-nam were once CTRU’s Formidable Quartet. An incorrect decision in an operation caused the breakup of their friendship. And the quartet went their separate ways. Fast-forward to the present and an indiscriminate homicide again brings the quartet together. But there are still certain unresolved issues between themselves. POTT is Counter Terrorism Intelligence Cadre’s other elite task force. Team leader Fong Kwok-hei admires Po-po and asks her to become her subordinate. Team member To Siu-jie fancies her partner Yiu-yeung and finds out Po-po is Yiu-yeung’s ex-lover, so she “starts a war”. Successive explosions happen in the city. While investigating, Po-po asks prisoner-cum-hard criminal Dr. Hong’s for help, and the process is surprisingly easy. Actually, Dr. Hong has some trick up his sleeve.

A look at the hunt for California's Zodiac Killer, who murdered at least five people in the San Francisco Bay Area in the late 1960s and early '70s.