In December 1970 in Marseilles, France, a plainclothes policeman is observing former longshoreman turned entrepreneur Alain Charnier (Fernando Rey) chatting with some unsavory types. Charnier is being tailed by the undercover cop because he is a kingpin in smuggling heroin overseas - a fact that costs the cop his life when he later returns home and is shot in the face by Pierre Nicoli (Marcel Bozzuffi), Charnier's henchman.
Meanwhile, in Brooklyn, NY, a corner Santa is chatting with some children outside a seedy bar while a hotdog vendor completes a transaction. The Santa is Detective Jimmy "Popeye" Doyle (Gene Hackman) and the vendor is his partner, Detective Salvatore Russo (Roy Scheider), whom Doyle nicknames "Cloudy." The two narcotics cops are staking out the bar in hope of finding a pusher named Willie (Alan Weeks). When Popeye sees Willie in the bar passing some drugs to a companion, he starts singing to the children, his signal to Cloudy. Cloudy enters the bar and grabs Willie's buddy. Willie sees the commotion and suddenly flees outside, with Popeye and Cloudy in hot pursuit. They corner him in an alley and Willie slashes Cloudy's arm with a hidden knife and runs. The cops chase him on foot to a deserted lot where he trips and falls and is beaten by both cops before Russo implores Doyle to stop. Once the two cops calm down they confusingly interrogate Willie, trying to get information on his drug connection.
In France, Charnier finishes a day overseeing dock work and drives home to his seaside villa and his young trophy wife (Ann Rebbot), who obviously has expensive tastes. The two exchange gifts for their upcoming trip to the US. Charnier later meets his gunman Nicoli at a rendezvous point for an acquaintance of Charnier, TV personality Henri Devereaux (Frédéric de Pasquale). Devereaux is traveling to the US to make a film and has decided to aid Charnier's smuggling effort because he needs money. Nicoli believes involving Devereaux is a mistake, but is reassured by Charnier.
In NYC, Popeye and Cloudy sign off for the night and Popeye takes his reluctant partner to a nightclub called The Chez. Popeye notices one table in particular, populated by known narcotics connections who are being entertained by a free-spending young man whom Popeye describes as a "greaser." Popeye smells a drug deal underway and persuades Cloudy to help him tail the greaser and his companion, a big-haired blonde. Throughout the night they tail the two, watching them drop off a suitcase in Little Italy and then switch cars early the next morning from an attractive coupe to a beat-up sedan. They then drive to a candy store/luncheonette, "Sal and Angie's", in a working-class area of Brooklyn. Peering inside as the couple prepares to open for the day, Popeye and Cloudy notice that the blonde is now a brunette, having worn a wig the night before.
Realizing they are on to something, the two cops stake out the candy store for a week using audio surveillance. Cloudy poses as a photographer to question Angie. Combing records they find that the greaser is Salvatore "Sal" Boca (Tony Lo Bianco) and his wife is Angie (Arlene Farber). The candy store's income could not explain Sal's free-spending ways. The posh coupe is owned by Angie while the beat-up sedan is owned by Sal's brother Lou (Benny Marino), a garbageman in training at a facility on Ward's Island in the East River. All three Bocas have criminal records. The candy store is regularly visited by unsavory types from New Jersey, and Sal makes numerous trips to an expensive condo in Manhattan at which lives lawyer Joel Weinstock (Harold Gary), a known drug financier who bankrolled a heroin shipment from Mexico.
Popeye and Cloudy raid a junk-house bar. One Afro-haired patron (Al Fann) talks back at Popeye and is hauled into a men's room to be beaten up - actually cover so Popeye can debrief his informant, who reveals that a big shipment is due within a few weeks that will satisfy everyone in the city. In order to make the ruse look convincing, Popeye punches his colleague in the jaw, a bit too enthusiastically.
Popeye's boss, Walt Simonson (Eddie Egan, the real-life inspiration for Popeye Doyle), is reluctant to let the two cops continue with their investigation of Boca, pointedly reminding Popeye of a previous case where his hunches backfired. But with Joel Weinstock, whom the police have long wanted to arrest, potentially involved, Simonson relents and goes to court for a wiretap on Boca's house and candy store. The federal Bureau of Narcotics and Dangerous Drugs (BNDD) now becomes involved and assigns Agents Bill Mulderig (Bill Hickman) and Bill Klein (Sonny Grosso, the real-life inspiration for Cloudy Russo), who've worked with Popeye before; Popeye and Mulderig are at constant loggerheads because Mulderig blames Popeye for the death of a policeman in a previous case and doesn't believe Popeye's hunches to begin with.
Charnier, Nicoli, and Devereaux arrive in NYC and Devereaux brings with him Charnier's Lincoln, signed for in Charnier's stead. They speak fair English, but nonetheless have an interpreter, La Valle (Andre Ernotte), with them. La Valle escorts Charnier to a police auction of impounded cars and identifies Lou Boca as the scrap metal buyer for Charnier's business (suggesting how the Bocas may have linked up with Charnier).
After several days of monitoring mundane conversations, the wiretap finally brings Popeye and Cloudy their first break - Charnier phones Sal to arrange a 12 o'clock meeting the next day. Popeye, Cloudy, and Mulderig tail Sal to midtown Manhattan, where they spot Sal meeting with Charnier and Nicoli. While Mulderig follows Sal, Popeye and Cloudy tail Charnier, dubbed "Frog One," and Nicoli as they walk through the city. The Frenchmen stop to eat at an expensive restaurant, which the cops observe while standing outside in freezing temperatures and eating bad pizza with worse coffee. Later, Popeye finds out that Frog One is staying at the Westbury Hotel, but Mulderig still doesn't believe Popeye is on to anything, leading to a brief argument.
At Joel Weinstock's condo, a young dope chemist (Pat McDermott) tests a sample of Charnier's heroin and it measures to 89% pure. There are sixty kilos due to arrive; when cut down into "dime bags" it will total out to $32 million with a half-million cash down payment. Weinstock, however, wants to wait before the switch is made, much to Sal's displeasure as Sal fears that Charnier will abort the deal if Weinstock drags it out too long.
The next day Popeye arrives at the Westbury just in time to see Charnier breeze right by the distracted Mulderig and Klein and walk into the city without a tail. Popeye tails Charnier himself, almost loses him at a flower shop, but then picks him up again at the Grand Central subway station. They play a cat-and-mouse game on the platform, but the wily Charnier manages to hop back on a train at the last moment and waves goodbye as the furious Popeye futilely runs after the train.
Charnier meets Sal in Washington DC - Sal followed there by Klein - where Charnier insists that the deal must be consummated by the end of the week, despite Sal's protests that his mob pals want to wait. On the flight back to New York, Charnier expresses his worries to Nicoli, who points out that Sal's concern about the police is warranted. The Frenchmen agree that Doyle is the main problem, and Nicoli volunteers to assassinate Doyle. Charnier reluctantly agrees, unaware that a fight has erupted between Popeye and Mulderig, and that Popeye has been taken off the case by a furious Simonson.
The dejected Popeye returns to his Brooklyn apartment building, where he is fired upon by Nicoli from the roof. Popeye manages to enter the building and pursues Nicoli to the roof, and then back down when he sees Nicoli fleeing. Nicoli runs to a nearby elevated train station and boards the train while Popeye screams for a uniformed transit policeman on board to stop him. As the train leaves the station, the transit policeman follows Nicoli as he moves forward through the train. Popeye commandeers a Pontiac Le Mans from a flabbergasted citizen. Nicoli kills the transit cop and seizes the motorman, forcing him to keep the train going through all the regular stops. Popeye furiously pursues in the car, barely escaping as other cars sideswipe him, and he nearly strikes a woman pushing her child in a baby carriage. Nicoli then kills the conductor who tries to intervene, and the crowd on the train flees while the terrified motorman collapses with a heart attack, locking the train on a collision course with a stopped train. The two trains crash and passengers, including Nicoli, are thrown about. Despite injuries and losing his gun, Nicoli slips out undetected - by everyone except Popeye. Nicoli starts down the stairs but is cornered by Popeye, and when he tries to flee he is shot dead.
Popeye and Cloudy, now back on the case, tail Sal as he takes the Lincoln from a parking garage to a side street. The police stake out the car all night; at 4:10 AM a gang of thieves tries to strip it, but they are arrested by a horde of policemen and the car is towed to a garage to be searched as evidence. The mechanic (Irving Abrahams), cannot find any narcotics in the car, but Popeye refuses to believe it. While Devereaux (who signed for the car) and La Valle argue with the garage desk sergeant, Cloudy notices a 120-pound discrepancy between the car's listed weight and actual weight. The mechanic reveals one area he didn't open up - the car's rocker panels underneath the doors. Popeye chews him out and then helps open up these panels, and the stash is found. The car is replaced (either repaired or the department acquires another, intact one), the stash replaced, and it is returned to Devereaux, while the police now wait for the dealers to make their final move.
Devereaux meets again with Charnier and is reluctant to do any more favors, until Charnier reveals that Devereaux is now an accomplice - to Devereaux's surprise and horror. Devereaux walks away, but Charnier takes the car himself and drives it to Ward's Island, where Lou Boca directs him to an abandoned factory building. There the heroin stash is revealed and tested positively. The stash is hidden inside the building and cash payment is hidden in the rocker panels of the junker car Lou Boca bought. With the deal completed, the Bocas briefly celebrate and Sal drives Charnier back to the city - and right into a police roadblock led by Popeye. Sal drives back to the factory with police in pursuit, and the mobsters hide inside the main building while Charnier hides in a secondary building. A gunfight ensues, in which Sal Boca is shot dead. Popeye hunts for Charnier inside the dilapidated warehouse. Cloudy joins him as Popeye appears to have cornered Charnier, but as the two cops approach the room Popeye sees someone from another door. He opens fire before Cloudy can corner the now-dead man - who turns out to be Agent Mulderig. Determined to get Frog One at any cost, and not caring that he just killed a Federal agent, Popeye strides through the warehouse, believing the Frenchman is still in hiding. After he rounds a corner a single gunshot is heard.
In an epilogue, it is revealed that Weinstock and the surviving Bocas either skated or received peripheral sentences while Henri Devereaux wound up in federal prison for four years; Charnier escaped and is believed to be living in France, and Doyle and Russo were suspended from narcotics duty.
冤家搭档破获法国大规模贩毒案
