In Miami, a gang of criminals successfully steals a huge supply of heroin from the police. It's up to narcotics cops Mike Lowery (Will Smith) and Marcus Burnett (Martin Lawrence) to find the drugs to save their jobs. A prostitute friend of Mike's responds to a call from one of the careless criminals, and brings her friend Julie (Tea Leoni). The bad guys murder the prostitute, but Julie witnesses it and gets away. Due to a mix-up, Marcus must pretend to be Mike to keep Julie happy, and so Mike and Marcus must pretend to be each other, protect Julie, find the bad guys and the drugs, and avenge their friend, all the while trying not to blow up half of Miami.