When a pack of sabre-toothed tigers wants revenge on the humans that killed some members while defending their infant. When they plan to exact their revenge, the infant's mother takes it and ends up going over a waterfall. The infant survives and is found by a moody wooly mammoth named Manny, and a hapless sloth named Sid. Now, the tiger (Diego) must act like it wants to return the infant to it's tribe in order to lead a now bigger prize, Manny, to the pack. Along the way, the unlikely trio find out that you don't have to be the same kind of animal, to be a herd.