A street quarrel leads to the death of a gang leader's son and, seeking revenge on a rival boss, he calls on Liu, a fixer, to import a hit man from the mainland. Lai Fu, a tough and youthful hick assassin, arrives with a day pass. The cops, led by the morose Milo, hear about the killer and start a full-scale Christmas Eve operation to find both warring brothers and the assassin. Lai Fu rescues a hooker, Dan Dan, from a sadist and asks her to help him find his way around Mongkok. By nightfall, Liu has double crossed Lai Fu, the gangster bosses are hiding, the cops are everywhere, and Lai Fu and Dan Dan are on the run. A multilayered thriller set in the malevolent claustrophobia of Kowloon, One Night In Mongkok follows in the accomplished footsteps of the Infernal Affairs trilogy.