One morning in South Park, Colorado, a group of friends, including Stan Marsh, Kyle Broflovski, his adopted brother Ike, Eric Cartman, and Kenny McCormick, decide to visit the local movie theater to catch the latest film featuring Terrance and Phillip, titled Asses of Fire, a notoriously inappropriate Canadian flick. Despite the warning from Kenny's mother, Carol, who chastises him for missing church, the boys are determined to see the movie. When their attempts to purchase tickets to the R-rated film are thwarted, they resort to enlisting a homeless man to pose as their adult guardian.
After finally watching the film, the boys find themselves swearing like there's no tomorrow, much to the astonishment of their classmates. This newfound vocabulary soon leads to trouble when their parents discover their foul-mouthed behavior at school, prompting a ban on the film, which they ultimately disobey. The film garners the reputation of being a corrupting influence on American youth, yet the Canadian minister in charge of film ratings defends it, stating its intended audience was evidently not children.
Meanwhile, a bet between Kenny and Cartman leads to a shocking accident: Kenny sets his fart ablaze, resulting in a horrific incident that sends him to the hospital, where he meets an untimely demise due to a comical heart transplant done by Dr. Gouache, who substitutes Kenny's heart with a baked potato. Upon his arrival in Hell, Kenny is greeted by none other than Satan and his not-so-reliable companion, Saddam Hussein.
On the home front, Kyle's mother, Sheila, mobilizes the Mothers Against Canada (M.A.C.) movement, as tensions brew between the U.S. and Canada when Terrance and Phillip are arrested on charges of war crimes during an interview on a talk show hosted by Conan O'Brien. The escalating conflict culminates in Canada retaliating by bombing the Baldwins, which provokes President Bill Clinton to declare war. Sheila, eager to take action, is appointed Secretary of Offense, and she aims to implant V-chips in all the children to curtail their swearing.
As the situation snowballs, Satan foresees the war as a harbinger of the apocalypse, pledging that the execution of Terrance and Phillip will trigger his invasion of Earth. Desperate to prevent this impending doom, Kenny's ghost warns Cartman, but the boys find themselves struggling against their parents' uninspired resolve. To counter the chaos, Stan, Kyle, and Cartman band together with their peers to execute a daring rescue plan for Terrance and Phillip, even enlisting the help of the resourceful Cristophe, known as "the Mole."
As the children infiltrate the execution ceremony, constraints tighten, particularly for Stan and Kyle, who must distract the guards while Cartman tackles the alarm system. Tragedy strikes when the Mole meets a fatal fate at the jaws of guard dogs. Their desperate pleas for assistance are ridiculed as the execution looms closer, culminating in an unexpected full-scale battle when Canada strikes back. In the heat of the moment, Cartman's sneeze inadvertently disables his V-chip, leading to a chaotic yet brave stand against oppressive government measures.
Things reach a fever pitch when the execution unfolds and tensions rise, pushing Stan to confront Sheila about her misplaced priorities, blaming her scapegoating for the mess they find themselves in. Just as hope flickers, Sheila makes the grave decision to shoot Terrance and Phillip, unknowingly fulfilling Satan's ominous prophecy. A power struggle ensues as Saddam's arrogance leads to a dramatic showdown, with Cartman wielding newfound energy—ultimately resulting in Satan's wrath.
In a moment of gratitude towards Kenny, Satan grants him a wish to restore everything to what it once was, bidding farewell to his friends. As the Dust of War settles, South Park miraculously returns to its original state, healing old wounds as unity prevails between Americans and Canadians. The story wraps up with Sheila and Kyle reconciling, and Wendy's affections being returned to Stan, as Kenny, rewarded for his bravery, finds himself welcomed into Heaven.
