The Special Duties Unit (SDU), led by Joe Ma and consisting of team members Him Law, Oscar Leung and Mandy Wong, continue to work coherently together. Still, new challenges constantly come up, including having to adjust to the different working style of the new Chief Inspector (Timmy Hung). During one particular hostage rescue mission, Joe encounters Linda Chung, an undercover agent who is being chased by the triads. Her resourcefulness and bravery leaves a deep impression on Joe. He helps her return to the Criminal Intelligence Bureau (CIB) and they gradually develop romantic feelings. But Joe is uneasy about Linda's deceptive behaviour, as if she is hiding a secret. In addition, his leadership of the SDU is questioned when a team member is reprimanded after a failed mission. Seeing the growing internal strife, Joe decides to resign. Meanwhile, Linda resorts to any tactic to find the person who betrayed her as an undercover, including using intelligence reports which put the SDU team at risk. Faced with so many imminent threats, how will Joe and the SDU team work together to solve these problems?