The Ice Age is coming to an end, and the animals are delighting in the melting paradise that is their new world. Manny, Sid, and Diego quickly learn that the warming climate has one major drawback: a huge glacial dam is about to break, threatening the entire valley. The only chance of survival lies at the other end of the valley. So the three heroes, along with a mammoth named Ellie and her two "brothers" -- possums Crash and Eddie -- embark on a mission across an increasingly dangerous landscape towards their salvation.