The drama follows the lives of undercover police agents who must live a double life in secrecy. Not knowing when they can return to their normal life, they must also endure the constant fear of being uncovered by those they are assigned to infiltrate. However, this time their lives are put in danger when it is discovered that a mole lives within the police force.

In 2010, Cheuk Hoi secretly travels to Bangkok to conduct a drug operation with his undercover agents in Thailand. However the success of the mission had cost all of Cheuk Hoi's undercover agents to be killed in a sea of fire. Meanwhile back in Hong Kong, his good friend CIB Inspector Lai, is killed for unknown reasons, leaving Cheuk Hoi to take charge of a female amateur cop who is not yet offici...

After completing his three-year undercover mission, Xue Jiaqiang returned to Hong Kong to open a foot bathing shop and continue to collect intelligence. Zhang Jizi, chief inspector of the criminal intelligence section, suspected that Zhuo Kai had been thrown into the underworld after he was released from prison and carried out comprehensive surveillance on him. Jia Qiang and Zhuo Kai were involved...