As Dean Higgins of Medfield College grapples with the fallout from Prof. Quigley's extravagant science class, he uncovers the outrageous costs stem from an unusual experiment involving feeding a cow bizarre concoctions in a misguided attempt to fatten it. Infuriated by this discovery, Higgins promptly dismisses Quigley and threatens expulsion for his students. In a fit of rage, he storms out of the classroom, slamming the door, unaware that his exit triggers a series of unexpected events. Dexter Riley's chemical experiment inadvertently combines with Richard Schuyler's vitamin cereal mix, creating a surprising new result.
The following morning, Dexter samples the now-tainted cereal and is astounded to find that it grants him incredible superhuman strength. This astonishing change isn't confined to just humans; their lovable house pet also gains remarkable physical abilities. As Dexter demonstrates his newfound strength by effortlessly lifting an overweight student along with Schuyler in a chair, Higgins seizes this chance to turn Medfield's fortunes around and prevent his firing by the Board of Regents.
Determined to capitalize on this discovery, Higgins pays a visit to Aunt Harriet Crumply, president of the Crumply Crunch cereal company, bringing the formula-enhanced cereal with him. He persuades her of its potential to transform sports, and together they devise a plan to face off against Krinkle Krunch, Medfield's rival cereal brand owned by the devious Mr. Kirwood Krinkle, in a weight-lifting contest featuring rival teams. State College, equipped with substantial resources, emerges as the favored contender in this high-stakes battle.
Meanwhile, as Krinkle’s inside man Harry provides him with inside information, a nefarious scheme unfolds. Recently paroled A.J. Arno and his crew are recruited by Krinkle to steal the coveted formula. Operating under the cover of night, they manage to sneak onto the campus, narrowly avoiding detection as they attempt to seize the prized mixture. However, their plan unravels when they mistakenly kidnap Schuyler, believing that Dexter's chemical is the actual key, rather than Schuyler's vitamins. The abducted victims are taken to Chinatown where they endure psychological manipulation aimed at retrieving the formula.
Once they have extracted the information, Krinkle’s henchmen hypnotize Schuyler, instructing him to return home and keep quiet about his captivity. Unbeknownst to them, this leads to an unforeseen event: Schuyler inadvertently takes control of a police vehicle, causing a chaotic high-speed pursuit that lands him in jail. Meanwhile, Krinkle decides to sample the formula himself, only to discover that, lacking Dexter's chemical, the cereal offers no superhuman strength, leaving him with a rather embarrassing hand injury instead.
As Krinkle angrily conveys his frustration to Harry over the phone, the reality hits him—if Medfield remains unaware of the formula's compromised abilities, they could be in for a devastating loss in the weight-lifting event. This realization triggers a pivotal turn of events, as Dexter finally comprehends the importance of his formula and sets out to retrieve it.
In a bold move, Dexter commandeers the Dean's classic car, racing toward the lab, only to find himself confronted by A.J. Arno and his thuggish aides. Undeterred, he consumes some of the formula, empowering him to effortlessly defeat the attackers, with Harry's help clearing the remaining henchmen like bowling pins.
As time runs short, Dexter learns through a radio announcement that he only has four minutes to return to the competition, or face disqualification. In a moment of ingenuity, he pours some of the formula into the car's gas tank, unleashing a surge of speed as the vehicle races forward, losing parts along the way. By sheer luck, Dexter arrives at the contest just in time, albeit in a vehicle that is now a mere shadow of its former self.
Though Medfield seems to lag behind, Dexter taps into his remaining superhuman strength to lift an astounding 1,111-pound weight, clinching victory for Crumply Crunch and Medfield. As the dust settles, Higgins and Quigley find themselves reprieved from any severe consequences, A.J. Arno is carted back to prison, and Krinkle suffers yet another humiliating defeat, his hand irreparably hurt after making the error of indulging in the wrong cereal.
