Miami detectives Marcus Burnett (Martin Lawrence) and Mike Lowrey (Will Smith) investigate $100 million of seized Mafia heroin, which was stolen from a secure police vault. Internal Affairs suspects that it was an inside job and threatens to shut down the entire department unless they recover the drugs within five days.
Lowrey asks one of his informants and ex-girlfriend Maxine "Max" Logan (Karen Alexander) to look for people who are newly rich and therefore suspects. She gets herself and her best friend Julie Mott (Téa Leoni) hired as escorts by Eddie Dominguez (Emmanuel Xuereb), a former crooked cop. The party is interrupted by Dominguez's French drug kingpin boss Fouchet (Tchéky Karyo) and his henchmen Casper, Ferguson and Noah. Dominguez and Max are killed, while Julie manages to escape.
At the police station, Julie insists on talking only to Lowrey, who is away. Knowing she never met Lowrey, captain Conrad Howard (Joe Pantoliano) forces Burnett to impersonate Lowrey to talk to her. At her apartment, Burnett and Julie are attacked by one of Fouchet's henchmen, whom Burnett kills. When they rendezvous with Lowrey, Burnett and Lowrey have to impersonate each other, and they keep it up in Julie's presence.
Looking through mugshots, Julie identifies Noah as one of the henchmen. The trio go to Club Hell, one of Noah's known hangouts. After being spotted, Burnett knocks Casper unconscious during a bathroom fight. Julie tries to kill Fouchet but Burnett stops her. In the ensuing car chase, Lowrey kills Noah. The three manage to get away, but are caught on camera by a news helicopter and later seen by Burnett's family.
Lowrey and Burnett meet their old informant Jojo (Michael Imperioli) and learn about the location of the chemist who is cutting the stolen drugs. The three return to Lowrey's apartment, where Burnett's wife confronts them and accidentally reveals to Julie they have been impersonating each other. Fouchet's gang show up and kidnap Julie.
Lowrey and Burnett's department is shut down by Internal Affairs. Despite being reassigned, Howard delays the order, giving Lowrey and Burnett more time to solve the case. They access Dominguez's private police database profile and learn that the police secretary Francine is Dominguez's former girlfriend.
Burnett, Lowrey and two other Miami detectives (Nestor Serrano and Julio Oscar Mechoso) head to Opa-locka Airport. After a fierce shootout, they kill all of Fouchet's henchmen, including Casper and Ferguson, and rescue Julie. They chase a fleeing Fouchet and force his car into a concrete barrier. As Fouchet tries to flee, Lowrey shoots Fouchet in the leg and arrests him at gunpoint. After a tense conversation with Burnett, Fouchet surreptitiously draws a gun but is shot before he can kill Lowrey or Burnett, avenging Max and Dominguez. An exhausted Burnett leaves Julie with Lowrey and heads home, eager to be reunited with his wife.
