Five prisoners - Teapot, Curly, Exhaust Pipe, Vaseline, and Rookie meet in their cell to form a friendship. Rookie assumes the leadership of the group, whilst Teapot is bullied by the others (in the later films, Roundhead, played by Eric Tsang, is the group's victim and Hung's character is the leader). Following their release, they team up with Curly's beautiful sister, Shirley, and form a company called the Five Stars Cleaning Co. read moreWhile most of the group attempt to vie for Shirley's affection, Teapot ultimately forms a relationship with her.
A sixth convict, the wealthy Jack Tar, is released on the same day. Upon his release, he commences work on his next criminal project: trading counterfeit US and Hong Kong currency with an American crime boss. Jack sends his chauffeur to do the exchange at a skating competition, but the chauffeur's insecure attitude attracts the attention of two muggers. The muggers steal the briefcase containing the counterfeit US money and take off. Police officer CID 07 (Jackie Chan) attempts to recover the briefcase containing the phony money, but the case accidentally ends up in the Five Stars Cleaning Co. van. CID 07 continues his pursuit of the muggers, which results in a massive freeway pile-up.
Teapot and his friends are unaware of the mishap, and drive away with the case. The chauffeur informs Jack, who orders his men to search for them. Later, Jack hosts a party at his mansion. Teapot and his friends decide to gatecrash, hoping to expand their business with the wealthy guests. They successfully enter the mansion undetected, and while socializing with the other guests, Jack privately meets a Triad boss to discuss a new deal for the counterfeit plates. A bodyguard then realizes the Five Stars Cleaning Co. are there, and alerts Jack, who interrogates Curly. Curly insists he has no knowledge about the case, and the ensuing ruckus causes a physical confrontation between the friends and Jack's bodyguards. The friends narrowly escape, only to be kidnapped by the Triad boss, who secretly wants to cut off the deal with Jack and obtain the plates himself. He orders the friends to give up the case, and holds Shirley hostage. The friends return home and finally discover the case. When they leave to make the dropoff, however, Jack's men arrives. Teapot, Exhaust Pipe, and Vaseline engage them in battle, while Curly leaves to fetch the Triad boss and Rookie goes for help. The Triad boss and his bodyguards arrive, where Jack learns of his motives and turns the fight against him instead. The police arrive, led by Rookie, who reveals himself to be undercover. They arrest Jack and the Triad boss and their men and rewards the friends for their assistance.