When the valley where they live is threatened by the melt of the surrounding ice, the mammoth Manny, the sloth Sid and the saber-toothed tiger Diego advise the other animals to look for shelter outside the place. While escaping, the trio meets Ellie, a female mammoth that believes she is an opossum like her two mischievous brothers. Meanwhile, the squirrel Scrat tries to retrieve his walnut in the most unusual situations.