The day begins with a stunning blow for Beavis and Butt-Head: their cherished television has vanished from their modest home. Determined to retrieve their beloved set, the dynamic duo embarks on a misadventure marked by continuous setbacks. In their search, they fortuitously stumble upon a motel that seemingly offers a TV in every room—a twist of luck that soon unravels. Muddy Grimes, who has a much different agenda, mistakenly believes that Beavis and Butt-Head are professional hitmen and offers them a hefty $10,000 to "deal with" his wife, Dallas, in Las Vegas. Butt-Head naively interprets this as a chance to get cozy with Dallas herself, convincing themselves that their newfound wealth will allow them to buy an even shinier TV.
As Muddy takes them to the airport, Beavis and Butt-Head remain blissfully unaware of their true mission. Once in Las Vegas, they settle into their hotel, where their eavesdropping leads to a dramatic confrontation with Dallas, who, armed and dangerous, offers them $20,000 to "handle" Muddy instead. The boys find themselves in a comical predicament, vying to see who can claim the reward first, completely missing the gravity of their misunderstanding.
Dallas then takes things to a darker level by placing a stolen biological weapon, the X-5 unit, in Beavis' shorts and instructs them to meet her at the U.S. Capitol for a crucial meeting. However, her real goal is to finish off the duo and retrieve the deadly weapon. Meanwhile, their antics on a tour bus inadvertently cause chaos at Hoover Dam, landing them a spot on the FBI's most-wanted list.
Their misadventures escalate as they end up on the wrong bus, joining a horrified group of nuns. Eventually abandoned in the Petrified Forest National Park, they encounter two former Mötley Crüe roadies—unbeknownst to them, these wild individuals are actually their biological fathers.
As Muddy grapples with his hunt for the boys, he crosses paths with the real hitmen involved in the theft of Beavis and Butt-Head's TV. Fueled by anger, he vows to track down the duo. Yet the hitmen—having long discarded the TV—leave the treasured piece of equipment behind at the motel. Upon waking, Beavis and Butt-Head find their TV returned; however, their journey is far from over. Dehydrated and weak, they set off across the desert, haunted by visions of their past misadventures. In a twist of fate, Beavis takes a risky bite of a peyote cactus, plunging into a hallucinatory realm where they star in a heavy-metal music video.
Muddy, desperately trying to keep the boys from meeting Dallas, seeks to maintain control over their chaotic path. But when they manage to escape his clutches and leap from his trunk, they cause a massive 400-car pileup on the Virginia interstate in their wake. Once the dust settles, they hop back on their trusty tour bus, making pit stops at iconic locations including the Capitol Building, before finally arriving at their ultimate destination: the White House.
In a twist of fate, Muddy's attempt to thwart Dallas' plans fails spectacularly when she seduces him in a parking garage, leading to a situation that ends with both falling into the hands of the ATF. Unbeknownst to them, Beavis and Butt-Head's escapades have drawn the attention of the authorities, leading to their unanticipated presence at the White House.
As tensions rise, Beavis undergoes a transformation into his hyperactive alter-ego, Cornholio, after indulging in a potent mix of caffeine and sugar. In this chaotic state, he bursts into the Oval Office, accidentally activating a military alert. Meanwhile, Butt-Head's futile attempt to impress Chelsea Clinton ends in rejection, forcing him to make a hasty retreat through her window.
As the pandemonium intensifies, Beavis finds himself at Tom Anderson's travel trailer, caught in a rather embarrassing situation. This incident leads to a misunderstanding by the ATF, who prepare for an all-out assault, believing Beavis has acquired a dangerous weapon. However, Anderson’s timely intervention and the revelation that Beavis' pants are missing ultimately defuse the climactic crisis.
In the aftermath, Anderson, Dallas, and Muddy face arrest, while Anderson's wife endures an embarrassing cavity search. In an unexpected twist of events, Flemming declares Beavis and Butt-Head the heroes of the hour, awarding them honorary ATF agent status courtesy of President Bill Clinton himself.
Upon returning to their home in Highland, the boys feel a sense of disappointment and emptiness, having failed to achieve any romantic success or financial gain. Yet, a surprise discovery of their lost TV re-ignites their enthusiasm, leading them to stroll off into the sunset—grumbling and squabbling over their cherished possession that brought them back to life once more.
