Senior Forensic Chemist Jack "Pro Sir" Po (Wayne Lai) is the head of the Forensic Department and is skilled at analysing criminal psychology. He has a unique view on human nature and is familiar with the structure of various firearms. Pro Sir works closely with Senior Pathologist Mandy Chung (Maggie Cheung Ho-yee) in a wide range of fields including psychology, anthropology, criminology and forensic science. CID Senior Inspector Ada Ling (Kate Tsui) and Sergeant "Wind" Lee Chin-fung (Ron Ng) work together cracking many murder cases. With a backbone of 12 cases, the forensic scientists, forensic doctors and the police all work together to accommodate each other to solve these cases. The perspective in this third installment is much wider than the previous two seasons with a legal standpoint in addition to the forensics.