16-year-old Cassie Sullivan tries to survive in a world devastated by the waves of an alien invasion that has already decimated the population and knocked mankind back to the Stone Age.

Set after the events of Continental Drift, Scrat's epic pursuit of his elusive acorn catapults him outside of Earth, where he accidentally sets off a series of cosmic events that transform and threaten the planet. To save themselves from peril, Manny, Sid, Diego, and the rest of the herd leave their home and embark on a quest full of thrills and spills, highs and lows, laughter and adventure while traveling to exotic new lands and locations.