5 HK cops (4 horny males) on vacation in Pattaya, Thailand, are told to contact an informant there but he gets murdered. They return to Hong Kong to contact his girlfriend and protect her. 3 other colleagues are busy fighting criminals.

A police informant sent a letter containing sensitive information on an illegal drug operation to his friend, Yi-Ching. While on vacation in Thailand, the informant is assassinated by the drug lord's henchmen and, to cover-up their operation, they attempt to eliminate Yi-Ching and double-agent Lau. Back in Hong Kong, police detectives Muscles and Ricky Fung are assigned to protect Lau and Inspector Barbara Woo is assigned to protect Yi-Ching. She takes her to the hideout of the "Five Lucky Stars" and also enlists their help in bringing down the drug operation.—Oliver Chu