As the first ice age slowly fades into history, a caveman couple, engulfed in a delicate moment of igniting a fire, finds their tranquility shattered by a massive earthquake that buries them beneath a collapsing cave. This cataclysmic event seems to signal the end of their prehistoric lives, but destiny has other plans in store.
Fast forward to 1992, where we meet Dave Morgan, portrayed by Brendan Fraser, a hapless teenager from Encino, trapped in a cycle of social insecurity and desperate for acceptance among his classmates. In stark contrast, his friend Stoney Brown, played by Pauly Shore, thrives in the high school environment, leaving Dave yearning for his childhood love, Robyn Sweeney, who now finds herself entangled with the popular jock Matt Wilson.
Everything changes for Dave when he discovers a massive block of ice in his garage while digging for a swimming pool. Unbeknownst to him, the ice holds a frozen caveman who will awaken due to the space heaters Dave carelessly left on unattended. Upon returning home with Stoney, they are greeted by a bizarre scene: the house is a mess, decorated with hand-painted murals, and a smoke alarm is beeping ominously. They soon find the caveman, whom they name Link, frantically trying to start a fire in Dave's bedroom. Initially terrified by the modern sounds and sights, Link calms down thanks to Stoney’s clever use of a lighter.
In the days that follow, Dave and Stoney make it their mission to teach Link the ways of 20th-century life. They concoct an elaborate story to convince Dave's family that Link is an Estonian exchange student, allowing him to enroll in school. Link's shocking antics and extraordinary athletic skills unexpectedly elevate Dave's social standing, enabling him to get closer to Robyn and incite Matt's jealousy.
However, Stoney's quirky influence begins to change Link's personality, creating tension between him and Dave. The rivalry reaches a climax at a skating rink when Matt confronts Link, igniting a deeper conflict. Faced with the reality of losing his prehistoric home, Link feels grief, prompting Dave and Stoney to comfort him and strengthen their bond.
As Link gains confidence, an exhilarating driving lesson ends with him taking control of the car, leading to an escapade that leaves Dave and Link in hot water with the law. Tensions simmer further on prom night, where Robyn's wish to attend with Link collides with Dave’s objections. Stoney steps in, challenging Dave’s dismissive attitude, resulting in a poignant moment where Dave sincerely apologizes, laying the groundwork for a stronger friendship.
Prom night unfolds spectacularly as Link and Robyn shine, while Dave decides to stay home. Meanwhile, Matt plots to ruin Dave's reputation by exposing Link's true identity as a caveman but fails miserably when an earthquake disrupts the party. In the end, when Matt attempts to disclose Link's origins to the crowd, skepticism from the attendees undermines his efforts, leaving him humiliated and paving the way for Dave and Robyn to mend their relationship.
With an infectious groove courtesy of Infectious Grooves, the trio leads an impromptu dance that captivates the partygoers. Post-prom, a pool party summons students to Dave's home, where a romantic kiss is shared between him and Robyn. Meanwhile, Stoney and Link stumble upon clues hinting at Link's past, leading them to a revelation in the bathroom where Link's long-lost girlfriend, who also survived the ice age's earthquake, awaits. Their reunion leads to an emotional embrace as she transforms into a modern woman, reflecting Link's journey of adaptation and acceptance.
