A martial arts instructor working at a police academy gets imprisoned after killing a man by accident. But when a vicious killer starts targeting martial arts masters, the instructor offers to help the police in return for his freedom.

Lau Ching Wan was in the force for almost ten years. He was very careless and was termed "Detective Idiot" by his colleagues. One day, he came to the knowledge that his boss, Christine Ng was a lesbian. Nevertheless, they became good friends and treated each other like brothers. Unfortunately, Lau fell in love with Ng's girlfriend.