- Undercover cop Muscles (Jackie Chan) enlists his childhood friends, the "Five Lucky Stars", to travel to Japan to help him catch a Yakuza group.
A corrupt Hong Kong cop (Lam Ching Ying) flees to Tokyo to join his fellow mobsters, whose headquarters are secretly built under an amusement park (filmed in Fuji-Q Highland). Two loyal cops, Ricky (Yuen Biao) and Muscle (Jackie Chan), travel there to apprehend him and uncover the mobsters’ lair, but Ricky is kidnapped in a fight. Muscle goes into hiding and calls his supervisor to send help; since the mobsters already have information on the officers of the Hong Kong Royal Police Force, Muscle asks to send his orphanage friends, nicknamed the Five Lucky Stars, over. The supervisor agrees and collects the five friends, who are all either petty criminals or low-wage workers. They refuse to aid the police, but the supervisor cunningly sets up a false story in the media that accuses the five of robbing a bank of millions of dollars, blackmailing them into helping. They ultimately agree when the supervisor teams them up with a rookie policewoman, Swordflower, who becomes an object of lustful target to the five. They travel to Tokyo and that night, Kidstuff (Sammo Hung), who is the Stars' most rational and talented member, and Swordflower go to Muscle’s apartment. After defeating some thugs, Muscle reunites with Kidstuff. The operation is to send phony money to the mobsters to allow the five to enter their lair, and that way they can get closer to freeing Ricky and apprehending the criminals. After a prolonged battle at the bowels of the amusement park, the criminals lose and the Lucky Stars receive a place to live back at Hong Kong as their reward.