In a cabin in the woods, Federal Bureau of Investigation (FBI) agents and Marcellino, a protected witness, are ambushed and killed by Chicago mobsters. When agent Harry Shannon investigates the crime scene, he finds his agent son, Blair, among the dead, and vows to get revenge. Elsewhere, former FBI agent turned deputy sheriff, Mark Kaminski, chases and arrests a man impersonating a police motorcycle officer. Afterward, he returns home to find his wife, Amy, decorating a cake. She is bitter that he quit his FBI job instead of fighting for reinstatement. Mark argues that if the matter had gone to trial, he would have lost and been prevented from accepting the post he now has. Amy throws the cake at her husband but misses. Later, she falls asleep on the sofa. Harry Shannon calls Mark and hints that if he helps with a difficult case he could receive a pardon and return to the FBI. They meet in secrecy and watch a videotape of special federal prosecutor, Marvin Baxter, questioning Chicago crime family boss, Luigi “Lou” Petrovita. Harry tells Mark that the recent raid was sanctioned by Petrovita. Mark recognizes Baxter as the man who forced him to resign from the FBI. Harry wants to coordinate an independent mission to topple Petrovita. If they succeed, Harry believes Baxter will allow Mark to return to the FBI. Harry provides Mark with information on Petrovita’s cronies and suggests that Martin Lamanski, owner of several illegal gambling establishments, may lead him to the crime boss. Harry reminds Mark to be vigilant. Elsewhere, Petrovita and Lamanski quarrel. Lamanski signals his assassins to shoot Petrovita and his associates. Petrovita escapes, and curses Lamanski’s incompetence as he drives away in a bullet-riddled sedan. Meanwhile, Mark goes to a casino at the Allerton Hotel to meet with Petrovita's associate, Paulo Rocca. Mark introduces himself as “Joseph P. Brennan” and establishes himself as Laminski's adversary. Rocca gives Mark $1,000 worth of casino chips and tells him to enjoy himself. Instead, Mark flirts with an attractive blonde named Monique and gives her the chips. When he leaves the hotel, three Rocca associates follow him into an alley. They scatter when an unmarked police car appears, leaving Mark to talk his way out of the situation as the police detective eyes his identification. Meanwhile, Martin Lamanski tips off FBI agents, and they raid a Petrovita safe house, confiscating drugs and cash and arresting eight men. Later, Paulo Rocca suggests they kill Lamanski, but Petrovita believes they will have to wait until the man lets down his guard. Rocca suggests they hire "Joseph P. Brennan" to replace an associate who was gunned down during Lamanski’s ambush at the waterfront. Mark meets up with Monique, and they go home together. They get drunk on champagne, and when he falls asleep in bed, she goes through his wallet. Mark wakes and hears her passing along his information to someone on the telephone. The following evening, Mark takes Monique to a party hosted by Rocca, where he is told that Petrovita wants to meet him. Meanwhile, Monique tells Keller that she has not found any useful information about their new acquaintance. Petrovita sizes up Mark during a brief conversation. After the party, Mark and Monique are ambushed by Lamanski’s men, but they escape. Sometime later, Petrovita insists they recover his cocaine and cash from police custody, but Rocca declares it is madness to rob a police station. Mark suggests they stage a bomb scare to clear the building. Mark later meets Harry Shannon, and reveals that Petrovita will likely eliminate Lamanski after reclaiming the confiscated contraband. Petrovita’s men call a bomb threat into the police. As the building is evacuated, Petrovita’s men, disguised as a bomb squad, break into the vault and remove the cash and drugs. Meanwhile, Mark and Max Keller chase Lamanski to the waterfront. The mobster's car crashes into an oil tanker and explodes. Petrovita’s men leave the station with their bounty. Later, Keller meets a crooked Miami police officer and learns that Mark is lying about his identity. At a funeral parlor, Petrovita meets special federal prosecutor, Max Baxter, and complains that an FBI informant has infiltrated his ranks. Baxter cannot confirm who the mole might be, but reveals agent Harry Shannon's interest in the case against Petrovita. Monique seeks out Mark and wants to talk, but he and Keller have been asked by Petrovita to kill a police officer, and he promises to contact her later. The two men approach their target, who turns out to be Harry Shannon. Harry and Keller shoot each other, before Mark kills Keller. Mark is concerned for Harry, who is badly wounded, but Harry assures him he will survive. Mark returns to the city and prepares an arsenal for a stand off at the rock quarry, a front for Petrovita’s drug business. At the property, a shoot out ensues. One by one, Mark kills Petrovita’s entourage, then chases the criminal to his office, and kills him. As Mark leaves, he notices Max Baxter sniveling in a corner. When Baxter tries to talk his way out of the situation, Mark hands him a gun and tells him to resign or be prosecuted. Baxter fires the gun, but Mark shoots him dead. Mark drives to the airport and gives Monique $250,000 to leave town and start a new life. Mark then returns to the FBI, and to his wife, Amy.