Infernal Affairs is a 2002 Hong Kong crime drama film directed by Andrew Lau and Alan Mak from a screenplay written by Mak and Felix Chong. The film stars Andy Lau, Tony Leung, Anthony Wong, Eric Tsang, Sammi Cheng and Kelly Chen. The film follows an undercover Hong Kong Police Force officer who infiltrates a triad and another police officer who is secretly a spy for the same triad. The film is the first in the Infernal Affairs series, followed by Infernal Affairs II and Infernal Affairs III.
