Several cops went undercover. Due to some issues, all undercover identities were wiped clean from the police database.

When a bomb went off unexpectedly during a police operation to disarm it, bomb disposal officer Poon Shing-Fung got caught in the blast and lost one of his legs. Poon decided to leave the police service. Three years later, the police suspect Poon, who was found in a coma at the spot of a terrorist bombing attack, of being involved in several bombing attacks in the past two years. Poon can hardly remember his past and even his own identity due to post-traumatic amnesia. He plans to escape to find out the truth. Meanwhile, knowing the terrorist organization's schemes of destroying Hong Kong landmarks, Poon, as the key person between the police and the terrorist organization, could possibly save or destroy lives of the innocent civilians in the city.