"Defection" is starred by Ruco Chan, Ron Ng, Yoyo Mung and Aimee Chan. As an international metropolis, Hong Kong may be attacked by terrorists at any time. In order to prevent possible terrorist activities in the territory, the Anti-Terrorism Special Service Team was established in 2009. All members are recruited from within the police force. They are the elite among the elites. They have the freshness of a highly intelligent and heavily armed force and the heroic spirit of a disciplined force. Many elites from different departments such as SDU, PTU, ASU, G4 and the Serious Crime Unit have been strictly screened and successfully admitted to the Special Service Team. They receive intensive training, including shooting, physical fitness, explosives handling, firearms, etc., and become a world-class heavy-armored elite force, the Anti-Terrorism Special Service Team. Everyone goes from training to mission operations. Facing different cases and crisis management, from misunderstanding to understanding, building trust and friendship among compatriots, depicting a series of touching stories of life and death and mutual trust between team members.