Lau's wife, Susan, is the daughter of the billionaire Chow Yuen-sing. One night, Lau and two accomplices break into his father-in-law's residence, where they kill Chow and his butler, Uncle Man. Later, Lau lures his partners-in-crime to a rundown house and murders them, after which he attempts to make the scene seem as though the two of them killed each other in a dispute over the loot. Susan is not convinced that only the two killers were involved, so she hires Yau to help her investigate further. She has also become paranoid after her father's murder, so Lau has to discreetly give her pills to calm her down and put her to sleep.