Zhang Zaishan is a Senior Inspector in the Explosive Ordnance Disposal Division of the Hong Kong Police Force. Seven years ago, he infiltrated into the criminal gang of Hong Jipeng, the most wanted criminal. During a robbery of a vault, Zhang revealed his identity as an undercover agent of the bomb disposal team, and with the help of the police, he successfully prevented the bomb from detonating, and wiped out the criminal organization of Hong Jipeng and his brother. After his return to work, Zhang was promoted to a bomb disposal expert in the police force.