Possum brothers Crash and Eddie set out to find a place of their own. Together with the one-eyed weasel, Buck Wild, they face the dinosaurs who inhabit the Lost World.
Desperate for some distance from their older sister Ellie, the thrill-seeking possum brothers Crash and Eddie set out to find a place of their own, but quickly find themselves trapped in a massive cave underground. They are rescued by the one-eyed, adventure-loving, dinosaur-hunting weasel, Buck Wild, and together they must face the unruly dinosaurs who inhabit the Lost World.
Dreaming of moving out and making their mark on the world, even though their adopted big sister Ellie believes they are not ready to be on their own, prehistoric possum twins Crash and Eddie summon up the courage to leave the nest after the events of Ice Age: Collision Course (2016). But it is a jungle out there. And before long, the tiny explorers wind up back in the dinosaur-ridden Lost World: the subterranean realm of expert survivalist Buck Wild, the extreme one-eyed weasel from Ice Age: Dawn of the Dinosaurs (2009), and a new megalomaniac villain bent on world domination. Do the reckless brothers have what it takes to survive reality?—Nick Riganas
In order to prove to the rest of the group that they are independent and reliable on their own, Crash and Eddie set out to live their own lives. However, when they reunite with Buck, they are caught in a situation that may cost them their lives.—RECB3
Crash and Eddie, eager to prove their daring, accidentally cause an avalanche during one of their extreme stunts, destroying the gang's summer habitat. Manny, Sid, Diego, and Ellie are furious, declaring the possums incapable of surviving on their own. Determined to prove them wrong, Crash and Eddie sneak out of the camp while the others are asleep.
The next morning, Ellie realizes they are missing and insists they search for them. Meanwhile, Crash and Eddie stumble upon the Lost World, a hidden land teeming with dinosaurs. There, they reunite with Buck, who saves them from raptors. Buck reveals that a Protoceratops named Orson, once bullied for his massive brain, has escaped exile and aims to dominate the Lost World. When they try to return home, they find that Orson has blocked the entrance with a boulder.
Seeking refuge, Buck takes Crash and Eddie to his shelter and explains his past. He recounts how he and his old team had established a peaceful watering hole for all animals but clashed with Orson, who believed in a world where the strong ruled the weak. After defeating Orson, they banished him to an island where he learned to control two raptors using fire.
Orson's raptors soon find Buck's hideout, but Zee, a gorilla and former member of Buck's team, rescues them using a knockout gas. Orson, now leading an army of raptors, attacks the watering hole, prompting Buck and Zee to evacuate the animals. Despite lingering tensions between them, Buck and Zee team up with the possums to seek help. They travel to the Lost Lagoon, where they summon Momma, a friendly Tyrannosaurus.
When Orson and his raptors attack again, Buck and Zee reconcile, realizing they must work together. Buck distracts Orson but is captured, allowing the others to escape. Determined to rescue Buck, Zee and the possums devise a plan. Meanwhile, Ellie, Manny, Sid, and Diego find the entrance to the Lost World and encounter Momma, who takes them to the watering hole.
At the watering hole, Orson prepares to feed Buck to the raptors as a warning to those who oppose him. Zee and the possums launch a rescue mission, freeing Buck and battling Orson and his army. The rest of the gang arrives with Momma, joining the fight. Buck attempts to reason with Orson, urging peace, but Orson refuses. Crash and Eddie discover that Orson controls the raptors with fire. Using their own fire, they disrupt Orson's control, turning the raptors against him and forcing him to flee.
With the Lost World saved, Manny, Ellie, Sid, and Diego apologize to Crash and Eddie for doubting them and invite them to return home. However, the possums decide to stay in the Lost World with Buck and Zee, feeling they have found their place. Though saddened, Ellie is proud of their growth and bids them farewell, knowing they will visit often.
