When Sid's attempt to adopt three dinosaur eggs gets him abducted by their real mother to an underground lost world, his friends attempt to rescue him. After the events of "Ice Age: The Meltdown", life begins to change for Manny and his friends: Scrat is still on the hunt to hold onto his beloved acorn, while finding a possible romance in a female sabre-toothed squirrel named Scratte. Manny and Ellie, having since become an item, are expecting a baby, which leaves Manny anxious to ensure that everything is perfect for when his baby arrives. Diego is fed up with being treated like a house-cat and ponders the notion that he is becoming too laid-back. Sid begins to wish for a family of his own, and so steals some dinosaur eggs which leads to Sid ending up in a strange underground world where his herd must rescue him, while dodging dinosaurs and facing danger left and right, and meeting up with a one-eyed weasel known as Buck who hunts dinosaurs intently.