In the quaint town of Scotland, Pennsylvania, lies a humble fast-food joint, Duncan's, which was bustling with life back in 1975. Among its loyal employees was Joe "Mac" McBeth, who found himself overlooked for a much-deserved promotion to manager by the scheming Douglas McKenna. Unbeknownst to others, McKenna was embezzling funds from the restaurant. One fateful day, Mac encountered three free-spirited hippies, one of whom was a self-proclaimed fortune teller. They confidently foretold a promising future for him in bank drive-thru management. This outlandish revelation ignited a spark in Mac and his wife, Pat, prompting them to play detectives. They clandestinely gathered evidence of McKenna's corrupt activities and shared it with Duncan.
Impressed with Mac's dedication, Duncan disclosed plans to transform his beleaguered burger joint into a lucrative drive-through. Captivated by this vision, Mac soon became entangled in a treacherous power struggle after Duncan was fatally injured in a staged robbery devised by Pat. The couple’s plot takes a turn for the chaotic when their attack on Duncan leads to an unexpected mishap involving a deep fryer, leaving Pat with scalding burns in the process.
The scene escalates when Investigator McDuff arrives, tackling the bizarre unraveling of events. A local homeless man, entangled in the theft due to found jewelry, is wrongfully blamed for the crime. Following the mayhem, Duncan's surprise posthumous gift to his eldest son, Malcolm, sets the stage for Mac and Pat to seize the restaurant, putting into motion their ambitious drive-through dream that soon captures the town's fascination.
With the returning Investigator McDuff, Scotland faces the aftermath, as the homeless man's name is cleared, and Mac and Pat adjust their focus toward Malcolm, now a pawn in their relentless struggle for power. Meanwhile, Mac's confidence transitions to paranoia, triggered by his friend Banko’s inquiries surrounding the origins of the drive-thru idea, leading him to an unsettling psychological decline characterized by a wild hallucination of the hippies, clad in deer attire.
On another front, Pat’s obsession with her burn intensifies, as an imagined deformity plagues her thoughts, although no visible scar mars her hand. Mac’s grasp on reality crumbles as he considers eliminating Banko, ultimately giving way to an impulsive act of murder.
The shocking news of Banko's gruesome death sends ripples through the town, just as Mac ascends to fame with a press event shadowed by scandal. In a surreal twist, during the conference, Mac conjures an apparition of Banko to pose a question, propelling him further into a spiral of madness that entrances a national audience.
Tormented by visions of the hippies and haunted by his actions, Mac becomes hell-bent on finding the trio, while Pat's detachment from reality grows, spiraling into belief that her hand is literally disintegrating. In a deeply troubling moment, Mac's mental stability deteriorates to incoherence, engaging in disturbing phone calls, including chilling plots hatched by the hippies against McDuff's family.
The climax pits Mac against law enforcement in a deadly encounter where he wields the sheriff's gun and commands an officer to fetch McDuff. A violent brawl ensues on the roof, resulting in a tragic fall, with Mac meeting a grisly fate impaled by his vehicle.
As Pat's delusions consume her, leading to a tragic end through self-harm, the ever-determined McDuff seizes the moment to fulfill his ambition of stepping into the culinary world, taking over the restaurant and exchanging chaos for calm.
