Hong Kong is rocked by a series of brutal murders. The victims are suspects of cold cases who have eluded arrest for many years. The group of killers, who call themselves "The Chosen Sleuths", are vigilantes who are taking justice in their own hands and openly challenging the Hong Kong police. In response, the police form a task force of their own "chosen sleuths" to stop the criminals. Jun Lee (Sean LAU) was a legend in the police force as an ace detective before the onset of his mental illness. Once nicknamed "The Chosen Sleuth", Jun now lives as a hobo on the streets after he was disgracefully dismissed from the force. To prove that he is not a lunatic, but the real "Chosen Sleuth", Jun joins the fight against "The Chosen Sleuths" to stop their elaborately laid plans. Racing against time, Jun and pregnant police detective Yee must race against time to solve cases both new and old to bring "The Chosen Sleuths" to justice.Three different teams of "chosen sleuths" in pursuit of justice are about to clash in an epic battle.