In Marseille, an undercover police detective is following Alain Charnier, a wealthy French criminal who runs the largest heroin-smuggling syndicate in the world. The policeman is assassinated by Charnier's hitman, Pierre Nicoli. Charnier plans to smuggle $32 million worth of heroin into the United States by hiding it in the car of his unsuspecting friend, French television personality Henri Devereaux, who is traveling to New York by ship.
Picking up two or three years after the original left off, narcotics officer Jimmy "Popeye" Doyle (Gene Hackman) is still searching for elusive drug kingpin Alain Charnier (Fernando Rey). Orders from his superiors send Doyle to Marseille, France, to track down the criminal mastermind and bust his drug ring. Once in France, Doyle is met by English-speaking Inspector Henri Barthélémy (Bernard Fresson), who resents his rude and crude crimefighting demeanor. Doyle then begins to find himself as a fish out of water in France, where he is matched with a language he cannot understand. Doyle is shown round the police station where he finds his desk is situated directly outside the toilets. He tells Barthélémy that he is not satisfied with this positioning and hopes it is not a joke at his expense. Barthélémy informs Doyle that he has read his personnel file and is aware of his reputation and especially hopes he has not brought a gun with him as it is strictly forbidden in France for visiting police officers from other countries to carry firearms.