A cop looking for a way out.

A kid looking for a way in.

Together they’re facing the crime of their lives.

Wing (Jackie Chan) is the Hong Kong police force's finest. Fung (Nicholas Tse) a disaffected youth, wants to follow in Wing's footsteps but his checkered background makes his dream of becoming a detective impossible.

When the ruthless Gang Of Five embark on a cop killing spree, Wing tracks them down only to be led into their trap. His colleagues, including the brother of his fiancée, are gunned down and Wing falls into an abyss of alcoholism and despair.

Fung finds Wing drunk in a gutter and masquerades as his new partner. Now guided by Fung's street smarts, the force's supercop sets himself on a no holds barred collision course with the most dangerous criminals in Hong Kong history.