As the Croods embark on their perilous quest to discover a new home, they are joined by their loyal friends, Chunky and Douglas, all while skillfully evading various hazards and hostile creatures. The formidable patriarch, Grug, grows increasingly troubled by the budding romance between his son Guy and daughter Eep, worried that their love may distract them from family unity.
Their adventure takes a surprising twist when Grug unexpectedly encounters a massive wall, leading his family into a paradise-like realm. However, they quickly find themselves under the influence of Phil and Hope Betterman, modern humans who were close friends with Guy's late parents. This new existence starkly contrasts with their wandering lifestyle, as the Bettermans showcase their technological prowess, polished manners, and subtle disdain toward the Croods.
Phil and Hope hatch a plan to persuade Guy to abandon his family and remain with them, convinced it would be in his best interest. Simultaneously, Grug finds himself ensnared in a series of uncomfortable situations orchestrated by Phil, who uses Eep's affection as leverage to keep Grug from leaving. Ugga, Grug's devoted wife, remains unaffected by Hope's manipulative tactics, prompting the couple to conclude they can no longer tolerate the condescension from the Bettermans.
Feeling stifled in her new surroundings, Eep befriends Dawn, Phil and Hope’s daughter, who has yet to experience the world beyond their secure walls. The girls persuade Chunky to take them on a joyride, which quickly descends into chaos. Upon their return, Guy reprimands Eep for her reckless escapade, creating tension between the couple.
During dinner, Grug inadvertently exposes Phil's scheme, leading the Croods to decide they have had enough of the Bettermans’ patronizing attitude and must go their separate ways. In an unexpected turn of events, Guy opts to stay behind with Phil and Hope, while the remaining Croods embark on a new adventure. Their departure soon gets interrupted by the vengeful Punch Monkeys, enraged over the absence of bananas from Phil's daily offerings. This leads to the capture of Grug, Phil, and Guy, leaving the other Croods and Bettermans to track their scent in a frantic chase.
As the unexpected group consisting of Grug, Guy, Phil, and their captors, the Punch Monkeys, converge at the monkeys’ lair, a captivating story unfolds. It becomes clear that the Punch Monkeys' initially aggressive demeanor stems not from their nature, but from an existential crisis triggered by Phil's irrigation efforts, which drained their land of vital water resources. This shortage serves as a dire warning from the Spiny Mandrilla, a gigantic creature with ape-like features, indicating that tranquility could only be restored if the monkeys offered the titanic being bananas.
While navigating treacherous terrains, the Croods and Bettermans find themselves stranded in an icy wasteland teeming with wolf spiders. In this extreme environment, Hope finally sets aside her biases against the Croods, recognizing them as true equals. This shared struggle enables the two families to forge an unbreakable bond, collectively adopting the name "The Thunder Sisters." Their solidarity ultimately leads them to reunite with Grug, Phil, and Guy just in time to thwart the Punch Monkeys’ plans to sacrifice their sons to the Spiny Mandrilla.
As tensions peak, Guy and Eep reconcile their differences, using a gigantic skull chandelier as an improvised catapult to send the Spiny Mandrilla crashing down to its doom. With danger averted, both the Croods and Bettermans emerge triumphant, having formed an enduring bond that bridges the gap between their species. The scene is set for a promising future, as the Bettermans extend an invitation to their new neighbors, the Croods, to settle on their land. As Guy and Eep adjust to life in one of the Bettermans’ bedrooms, the Punch Monkeys establish themselves as the new neighbors, heralding the dawn of a brighter, collaborative future for everyone involved.
