A deeply troubled man, portrayed by Michael Douglas, finds himself lost in the chaos of Los Angeles traffic on a scorching summer day. Frustrated and desperate, he abandons his car and begins an odyssey westward, determined to reunite with his estranged wife, Beth, and his daughter, Adele. With it being his daughter's birthday, the stakes of his journey could not be higher.
Meanwhile, Detective Prendergast is gearing up for his last day on the force, heading toward retirement. His day takes a turn when he discovers the abandoned vehicle belonging to the man known as D-Fens. Years ago, he had been relegated to a desk job after being pressured by his wife, and now he confronts the turmoil that swirls around D-Fens's erratic actions.
Desperate and short on coins for a phone call, D-Fens enters a Korean convenience store. A simple purchase spirals into chaos when the store owner demands 85 cents for a can of Coke. Angered, D-Fens lashes out, grabbing a baseball bat and wreaking havoc within the store. His rage grows as he pushes on toward Venice Beach, where he encounters two young gang members. In a tense confrontation, he defends himself, injuring one and successfully repelling the other.
As threats from these gangsters loom, D-Fens makes a bold call to his ex-wife, asserting himself as a looming presence at their daughter's birthday celebration. A failed drive-by shooting by the gang leads to further violence, but D-Fens manages to procure a weapon in the ensuing chaos. Haunted by fear and anger, he gives a briefcase, mistakenly believed to be his only means of sustenance, to a panhandler.
In search of food, he visits Whammy Burger, where a minor inconvenience leads him to brandish a submachine gun, causing terror among patrons and forcing the staff to reckon with their failure to meet his expectations. Following another outburst at a payphone, where he becomes enraged after being interrupted, Detective Prendergast begins to piece together the connection between these violent incidents.
Despite D-Fens's ex-wife's concerns, the police dismiss her fears as overblown, with the situation rapidly escalating as D-Fens interacts with various segments of society, leaving destruction in his wake. At one point, he visits an Army-Navy surplus store, where a misunderstanding with the Nazi owner leads to a deadly confrontation, solidifying D-Fens’s impending downfall.
As he ventures into a golf course, he confronts elderly players and expresses his disdain for their frivolities, before taking drastic measures that lead to a heart attack. Struggling with his moral compass, he continues down a reckless path, ultimately aiming for his former house where his ex-wife narrowly escapes.
Prendergast finally unravels the mystery and learns D-Fens's true identity—William Foster, who has lost his job and family. He races against time to stop a potential confrontation between D-Fens and his family. In a tragic climax on a fishing pier, a showdown ensues where D-Fens's tragic motivations are laid bare. As he attempts to regain a semblance of control and seek revenge, Prendergast intervenes, ultimately leading to a heart-wrenching conclusion. The detective acknowledges Foster's grievances about societal inequalities yet cannot condone his violent path. In an agonizing twist, Foster's self-destruction compels Prendergast to reconsider his retirement, suggesting that his fight against chaos is far from over.
