Following the parallel lives of Ming, a crooked cop who reports back to his Triad crime boss, and Yan, an undercover police officer who poses as a Triad member in the gang led by the same boss, Infernal Affairs is a meditative, hypnotic police drama of bluff and double-bluff. Yan has spent many years under the guise of a Triad member and he longs to return to a comparatively safe world of normalcy and regular police duty. Only Superintendent Wong, Yan's mentor, is aware of his identity, and he also happens to be Ming's superior. When Superintendent Wong's officers come face to face with the Triad gang, both leaders realise they have a traitor in their midst.

Classic Hong Kong action combines with both emotional and psychological sophistication to create a film of unique complexity and beauty.

Infernal Affairs uses a vibrating terseness usually found in the writer and director Michael Mann's work. The sophistication of the stylised minimalism here is dazzling.- New York Times