Originally an elite member of the Special Crime Unit in the Hong Kong Police Force, former cop Szeto Shun was forced to leave the force after getting implicated in an arson case. He is then hired at a security company, where he meets the intelligent Cheng Nik-hang. With their similar ways of thinking and work styles, Shun and Hang become close friends. Their superior also treats them as his left and right-hand men. Shun encounters private investigator Jenny, who triggers a memory he had long forgotten—new evidence in the arson case that had changed Shun’s life forever.