The story revolves around the lives of two NYPD police detectives, Det. Sgt. Deke DaSilva (Sylvester Stallone) and Det. Sgt. Matthew Fox (Billy Dee Williams) who work undercover, and a terrorist Heymar Reinhardt, alias Wulfgar (Rutger Hauer). In the prologue, set in the late night to early morning hours on New Year's Eve 1979, three armed assailants attempt a mugging on a supposedly unsuspecting woman, who turns out to be DaSilva in drag for a carefully planned sting operation to catch these muggers who rob elderly people. Fox immobilizes two of the suspects as Deke chases the third upstairs to the 174th Street (IRT White Plains Road Line) Subway Station platform and dares the man to cut him. Deke then incapacitates him places him under arrest.
The next scene takes place in London on the same day (five hours ahead because of the time zone difference), where Wulfgar (Rutger Hauer) bombs a department store after flirting with a young cosmetic salesgirl (Catherine Mary Stewart), instilling the will of fear in the surrounding society.
January 4, 1980. In New York City, DaSilva and Fox serve a high risk warrant in the Bronx. They raid a known drug distribution spot. The obvious corruption in the police department is exposed in the suspect's dialogue as a minor subplot. During the arrest, Fox becomes furious when one of the dealers tries to bribe him. He struggles with his overwhelming desire to shoot the unarmed man in front of witnesses, one of whom is a teenaged boy.
January 6. In London, Wulfgar converses with his contact at a party, Kenneth, who tells Wulfgar that Mercer, who we never see but come to know as the financier of Wulfgar's operations, is withholding money owed to Wulfgar because several children were killed in Wulfgar's latest bombing at the department store. Wulfgar quickly discovers that Kenneth had been held at Heathrow Airport in police custody, and has inadvertently led police to Wulfgar's location. Wulfgar viciously murders Kenneth and the policemen who had converged on the location.
Wulfgar flees to Paris where he meets his associate, Shakka Holland (Persis Khambatta) at La Sainte-Chapelle. Shakka remarks that La Sainte-Chapelle is a bad meeting place because it's next to (in real life too), the Palais de Justice, a courthouse in Paris. She informs Wulfgar that Kenneth's death was a rash decision, for the police found a passport that he'd brought to Wulfgar on his person. Wulfgar also realizes he has killed one of his own, and is now facing alienation from his allies. With his identity revealed to all European authorities, Wulfgar and Shakka visit a plastic surgeon, whom changes Wulgar's appearance. After the process, the surgeon becomes a liability, and is murdered by Wulfgar, who then flees to New York City.
The next day in New York, after having their undercover detail compromised by two uniformed officers, DaSilva and Fox are informed that they have been transferred from the Street Crime Unit and into a special Federal-State Unit. After a touchy moment with their ill-tempered superior, Lieutenant Munafo (Joe Spinell), they discover that their transfer orders came from the police commissioner, whom had received the orders from Washington D.C.. The fact that the two detectives served in Vietnam also play into this, making them two of the highest recommended candidates for the special unit.
Anti-Terrorist Action Command (A.T.A.C.) is assembled by INTERPOL British Counter-terrorist specialist Peter Hartman (Nigel Davenport). Hartman believes Wulfgar will come to the U.S. next primarily for the press coverage. Hartman schools DaSilva, Fox and a specially selected team of New York police on Wulfgar, Shakka, and terrorism in general. But the 'shoot-to-kill' policy that Hartman encourages doesn't go down well with DeSilva who didn't join the force to kill anyone. Hartman also makes a personal comment regarding DaSilva's ex-wife (Lindsay Wagner), which causes him to leave, but opening him up to the connections of the underground New York City
According to Hartman, Wulfgar wastes no time in becoming familiar with new surroundings. After completing the latter, Hartman states that Wulfgar, an aficionado for the vivid nightclub scene, will try to find safe housing for his arsenal. Sure enough, Wulfgar meets Pam (Hilary Thompson), a flight attendant, in a nightclub and moves in with her. Surprisingly enough, when she asks him what he does for a living, he tells her the complete and total truth: "I'm an international terrorist wanted on three continents." She takes it as humor.
That night, Wulfgar then announces his presence in New York by bombing several locations in the Wall Street area. Alone in her apartment while Wulfgar (known as 'Eric' to Pam), is away, Pam discovers his arsenal. Wulfgar kills Pam, and her death is the first break Hartman, DaSilva, and Fox get. Wulfgar has left behind a map of the Wall Street area.
According to Lt. Munafo and the forencic investigators, the location that had been bombed was marked. DaSilva and Fox investigate Pam's favorite nightspots and hope to find Wulfgar at one of them. They do. But, unsure of what he looks like since the plastic surgery, they hesitate. When DaSilva calls out Wulfgar's name, a shooting spree at the disco opens, with the two cops chasing Wulfgar through the club, and to the back streets and to a local subway station on the 6th Avenue Line, where Wulfgar takes an elderly woman on the platform hostage as a human shield. DaSilva again hesitates to shoot at Wulfgar (on the risking of hitting the woman hostage) and allows Wulfgar to board the train. Neverless, DaSilva and Fox climb aboard the rear of the train and chase Wulfgar through the cars until the train stops and he jumps off. Fox catches up to him, but Wulfgar slashes Fox's face with a knife, and gets away by jumping on anther passing train as DaSilva yells and curses at him. Fox recovers quickly -- DaSilva tells him his sharp reflexes kept Wulfgar from slashing his neck.
Wulfgar takes refuge in the basement apartment of a little grocery store, where it is revealed that Shakka is now in the United States to inform him that the NYPD and the United Nations delegation members have a description of him. Wulfgar tells Shakka that he is determined to find and kill the two police officers who chased him and begins to look over the files of all the A.T.A.C. police officers that the store owner brings to him.
January 17. The members of A.T.A.C. is protecting a United Nations function at the Metropolitan Museum of Art that has the earmarks of a potential terrorist target. Shakka infiltrates the party in disguise. She corners Hartman on an escalator and murders him.
Later that same day, Wulfgar and Shakka then hijack a Roosevelt Island Tram car carrying U.N. representatives. Fox, Munafo, and other officers hear about the hostage situation and take positions at both tram stations, while DaSilva takes off in a police helicopter to confront the stranded tram car over the East River. Wulfgar executes the wife of the French ambassador while DaSilva is watching from a hovering police helicopter as a penalty for the nightclub and subway chase. Wulfgar decides to release an infant onboard the car, and demands that DaSilva personally board the tramway to rescue it. DaSilva is winched up to the aerial tram and confronts Wulfgar face-to-face. DaSilva demands to know why Wulfgar killed the woman. "I wanted to", the sadist replies. However, he decides to spare his nemesis for the moment. DaSilva and the baby are lowered back down to a waiting barge. Wulfgar then makes a series of demands for the release of various terrorists in various countries as well as a bus to take him and the hostages to JFK airport where a jet will be waiting to take them out of the country, and he also demands that DaSilva drive the bus (implying that Wulfgar intends to kill DaSilva once they reach their destination).
The police agree to Wulfgar's demands for a bus to escort him and the hostages to the airport. That evening at nightfall, Wulfgar and Shakka bring the tram car down to Roosevelt Island and hide among the crowd of hostages from the tram. DaSilva waits until they try to board the parked bus before making his move. He plays back a recording of Hartman's lecture in which the terrorist expert denounces Shakka. In a rage, Shakka breaks from the hostages and is gunned down by Fox and various sharpshooters. Wulfgar returns fire on the police. He escapes, driving the bus off a ramp into the East River.
A search of the wreckage shows no sign of Wulfgar. Lt. Munafo leads the team where they find the store where Wulfgar has been staying and DaSilva finds that Wulfgar has gathered information on all participating members of A.T.A.C., including Fox, Hartman, and DaSilva. An address of his ex-wife, Irene is found on one of the printouts.
Wulfgar makes his way to Irene's house, hides outside, and sees Irene walk up to the house and go in. He breaks in, finds her washing dishes and sneaks up behind her brandishing a knife. But DaSilva has made it to Irene's first; he turns around, wearing his ex-wife's housecoat and a blonde wig, brandishing a gun. With nowhere to go, Wulfgar lunges at DaSilva who fires his revolver twice into the terrorist, blowing him into the street. Wulfgar lays dead on the stoop of Irene's rowhouse while DaSilva sits nearby looking on as it begins to lightly snow.