In this prequel to Infernal Affairs (2002), Chan Wing Yan has just become an undercover cop in the triads while Lau Kin Ming joins the police force. Both the triads and the police find an enemy in a rival crime boss.
"Ingeniously anticipating the action of the original, while intricately involving in its own right, this should help restore your faith in prequels. It's slick and atmospheric, knowingly directed and superbly played." - Empire
"The emphasis of IA2's script and direction is to allow characterisation to flourish, especially that of the adults. Wong and Tsang are magnificent and must now rank among Hong Kong's true stars, while Ng, Yu and popstar-turned-actor Chen are all strong." - Screendaily.com