Infernal Affairs (2002)

Infernal Affairs focuses on a police officer named Chen Wing-Yan (Tony Leung Chiu-Wai), who goes deep undercover into the Triad society, and Triad member Lau Kin-Ming (Andy Lau Tak-Wah), who infiltrates the police department. Each mole was planted by the rival organization to gain an advantage in intelligence over the other side. The more the moles become involved in their undercover lives, the more issues they have to cope with. The film follows their struggles with their double identities and their race to uncover the other mole. Eventually, they reach a deal to foil a drug deal orchestrated by an antagonist gangster named Hon Sam (Eric Tsang Chi-Wai), resulting in his death. However, Yan discovers that Ming was the mole, leading to a confrontation on a rooftop. Yan holds a gun to Ming's head, but is shot and killed by another mole within the police force, Inspector B (Gordon Lam Ka-Tung). Ming then shoots Inspector B dead and turns himself in to the police. The alternate ending shows Ming being arrested after being informed that evidence of his role as a mole has been found. He willingly surrenders and is taken into custody.