In a Hong Kong hospital, a French woman lies in critical condition after a gangland hit that killed her Chinese husband and two small children. Her father Costello (Johnny Hallyday) arrives from France and is immediately warned by police not to get involved, even as his daughter wordlessly pleads for his help. A stranger in a strange land and plagued by a failing memory, Costello sits stunned in his hotel room, scrawling the word vengeance over the bloody crime scene photos of his daughter's family. He soon crosses paths with three professional killers (To regulars Anthony Wong, Lam Suet and Lam Ka Tung) who work for the crass and flamboyant mob boss Fung (Simon Yam), and asks them to help avenge his family. But as the men get to know their new client, they learn that his past may not be as innocent as they had assumed. As Costello's memory problems worsen, the question becomes: what is the meaning of vengeance when you no longer remember either those who have wronged you or those you have lost?
With his debonair yet rugged good looks and piercing, pale eyes, Hallyday, a pop icon who has sold over 100 million records during his decades-long career and is considered by some to be the French Elvis Presley, adds pathos and depth to the enigmatic Costello. The craggy, lived-in face of Hallyday is as riveting as To's mad scenes of mayhem, which include a fierce nighttime shootout as clouds pass over the full moon and, shootouts being To's stock in trade, an epic battle in a junkyard that has to be seen to be believed.