NYPD Lieutenant John Moss [James Woods] pursues a serial killer known as the 'Party Crasher' through a crowded nightclub, but he cannot prevent the murder of a local drug dealer. During a press interview, Moss vents his frustration on camera in a blistering live broadcast, a moment that will ripple through the lives of everyone involved.
In Los Angeles, the ambitious Hollywood actor Nick Lang [Michael J. Fox] sees the interview and is struck by Moss's raw intensity. A former child star and pop-action icon, Lang longs for a genuine, serious role in a forthcoming cop drama, Blood on the Asphalt, and believes that studying Moss up close will help him project authenticity in his audition.
Lang leverages his industry connections to become Moss's unorthodox ride-along partner, posing as an experienced detective. Moss's supervisors pull him off the Party Crasher case to supervise Lang on low-risk assignments, a decision that infuriates him and fuels his lectures about the harsh realities, terror, and mistakes that come with real police work.
Lang quickly notices the strains in Moss's personal life, especially his difficulty dating Susan [Annabella Sciorra], a divorced single mother. Lang offers guidance and awkwardly wins over Susan and her daughter on a date, leaving Moss unexpectedly touched by the awkward sincerity of someone who seems to “get” the job—and the toll it takes on relationships.
Over the next few days, Moss tries to shed Lang, but Lang tests the limits of his imitation, pushing into dangerous territory to prove his acting chops. On a late-night pursuit through a deserted building, Moss, fearing Lang's safety, lends him a real firearm for self-defense. Believing Moss is in danger, Lang enters the building and accidentally shoots a bystander. Terrified, Lang agrees to help cover up the incident and plans to vanish town. The truth comes crashing down when Moss reveals the entire sequence was a controlled test to teach Lang about panic, self-doubt, guilt, and anger that accompany being a "real" cop. Enraged, Lang punches Moss and makes clear he intends to leave.
Lang later stumbles into a tense confrontation between Moss and the true killer, the Party Crasher, and he ends up saving Moss's life. The Party Crasher is wounded and placed in an ambulance, but escapes after killing several bystanders. Nick briefly corners him, radios their location, and is knocked out in the process. Susan visits Moss and confesses that a police career won’t guarantee a stable relationship, and she ends things.
Lang returns and argues that the Party Crasher will target Susan, even as Moss suspects the killer is staging a theatrical revenge for media attention. The threat comes to a head when the Party Crasher abducts Susan, drawing Moss and Lang into a perilous standoff on an advertising billboard that features Nick's latest film. A brutal fight ensues; Lang saves Susan and Moss from being shot, but Lang is wounded in the chest. Moss pushes the Party Crasher off the roof, then lectures Lang once more about the relentless dangers of the profession as he works to keep him conscious.
Months later, Moss and Susan are married and attend the premiere of The Good, the Badge and the Ugly. Lang survives his gunshot wound and channels the experience into a new drama, while Moss discovers that Lang’s best lines in the film largely echo his own relentless lectures—and jokes that Lang should have earned a writer’s credit.
