Tam (Aaron Kwok) is an impoverished private detective. One day, a guy nicknamed Fatty asks Tam to find a lady who wants to kill him. He leaves Tam a portrait and a large amount of cash without giving any other details. Tam cannot resist the offer and so his investigation starts.
Knowing that Sum, the lady in the picture, is a frequent visitor of a store where the picture was shot, Tam tries to get hints of her whereabouts from the storekeepers. He is told to find her through her mahjong playmates. Tam starts with Ming, but when he arrives at Ming's home, he finds Ming hanged in the living room.
As Tam continues to search for other mahjong playmates of Sum, he is shocked to find each of them murdered every time he is about to contact with them. He discovers a half-burned photo at one of the scenes. Tam realizes the suspicions behind the deaths and decides to protect the next target of the invisible murderer. The photo is the only clue for Tam to solve the case.
