During halftime of a televised professional football game, L.A. Stallions star running back Billy Cole (Billy Blanks) receives a phone call from someone named Milo (Taylor Negron), warning him to win the game at all costs, or "he's history". Cole ingests PCP and, in a drug-induced rage, brings a gun onto the field, shooting three opposing players to make it to the end zone. Cole then shoots himself in the head.
Private investigator Joe Hallenbeck (Bruce Willis), a disgraced former Secret Service agent who at one time was a national hero for saving the President from an assassination attempt, discovers that his wife Sarah (Chelsea Field) is having an affair with his best friend and sometime business partner, Mike Matthews (Bruce McGill). Hallenbeck's indifference frustrates his wife, who only did it to get his attention. Outside Joe's house, Mike is killed by a car bomb, after giving Joe an assignment to act as bodyguard for a stripper named Cory (Halle Berry).
At the bar where Cory works, Joe is approached by her boyfriend, former L.A. Stallions star quarterback James "Jimmy" Alexander Dix (Damon Wayans), who was banned from the league on gambling charges and allegations of drug abuse. After an argument where Joe and Jimmy scuffle, an annoyed Jimmy takes Cory from the stage while she is performing. Joe decides to wait outside, where he is knocked out by hitmen. Jimmy and Cory leave the bar in separate cars while Joe is escorted into an alley by one of the hitmen, who laughs at his jokes which enables Joe to kill him and escape. When Cory is hit from behind and stops to confront the other driver, she is shot dead by hitmen in the car. Jimmy is fired upon and pinned down, but is saved by Joe.
The next day at Cory's house, Jimmy and Joe find evidence of a phone conversation between the chairman of a Senate committee investigating gambling in sports, Sen. Calvin Baynard (Chelcie Ross), and L.A. Stallions team owner Sheldon "Shelly" Marcone (Noble Willingham). When the recorded evidence is ruined in Joe's faulty car stereo, Jimmy realizes that Cory tried using the evidence as leverage against Marcone to get his job back on the team, prompting Marcone to send the hitmen. Jimmy leaves to drive home in Cory's other car, but Joe correctly assumes Marcone had her other car wired to explode. Two hitmen arrive wanting the evidence Cory had, and Joe tricks them into blowing up the car, killing themselves, but also destroying the rest of the evidence. Joe reveals to Jimmy that when he was in the Secret Service, he was assigned to the Senator's protective detail. One night on duty he witnessed Baynard torturing a woman in a hotel room and assaulted Baynard to stop him, knocking out four of Baynard's teeth. Baynard would later have Joe kicked out of the Secret Service for refusing to cover up the incident. Joe and Jimmy then form an alliance to bring down Marcone.
Joe takes Jimmy home, where Jimmy meets Joe's abrasive daughter Darian (Danielle Harris). When Joe catches Jimmy attempting to use illegal painkillers in the bathroom, Joe kicks him out. As Jimmy leaves, Darian asks him to sign a football trading card. As he signs, she reveals that Joe had been a fan of his before he got busted, and ever since he was banned from the league, Joe has never watched another football game. He leaves her with the signed card, "To the daughter of the last Boy Scout."
The next morning the police, having learned of Mike's affair with Sarah, decide Joe must have killed Mike for revenge and move to arrest him. But Milo, Marcone's top henchman, captures Joe first, then shoots the cop who had come to arrest him using Joe's gun. Marcone explains to Joe that he intends to legalize sports gambling by buying votes and that Baynard holds the deciding vote in the matter. When Marcone also tried to buy his vote for this purpose, Baynard blackmailed Marcone, demanding $6 million or he would go to the police. Explaining it would be cheaper to kill the Senator, aware of Joe's history with him, Marcone informs Joe of his intention to frame him for Baynard's murder.
Joe is taken to a wooded area where he is photographed handing a briefcase containing money to Baynard's bodyguards. The money is then switched in the trunk with a wired briefcase. Joe is rescued by Jimmy and Darian and they manage to acquire both briefcases after running the bodyguards and Milo off the road; however, Milo survives and kidnaps Darian after Joe leaves her to wait for the police.
Heading to Marcone's stadium office to save Darian, they are caught and brought to Marcone's office, but Jimmy creates a diversion, allowing them to fight their way free. Knowing Milo will attempt to shoot Baynard, Joe goes after Milo while sending Jimmy to warn Baynard. Grabbing the game ball, Jimmy throws it at Baynard, knocking him down just as Milo starts shooting. Joe knocks Milo to the edge of the stadium light platform, where police shoot him several times, causing him to fall into the blades of a circling helicopter.
The suitcase of money is recovered and the fleeing Marcone, having escaped with the rigged briefcase, is killed when he opens it. The next day Joe and Sarah reconcile, and Joe and Jimmy decide to become partners. It is implied Baynard is finished.

Question: Who is Hallenbeck's wife Sarah having an affair with?
Answer: Mike Matthews
Alternative answer: Mike Matthews