A huge ice storm is approaching the prehistoric Earth and all of the animals are preparing by moving South. The only exceptions are Manfred, an agitated mammoth who wants to move North to his homeland, and Sid, a Megalonyx sloth abandoned by his family. Sid initially wants to go by himself but later teams up with Manfred for company and protection. They son run into Soto, the leader of a group of Smildon who wants to take revenge on a group of humans by eating a mother's baby son alive. After Soto's lieutenant, Diego fails to retrieve the baby, Soto sands him off to find the baby, who has fallen into the care of Manfred and Sid. Along with the main plot, this movie and the ones following feature a subplot on Scrat, a saber-toothed squirrel who is trying to chase an acorn.