20,000 years before, our planet is entering an ice age. All kinds of animals
begin immigrating to the south, seeking more warm climates. Sid, a sloth
who never stops talking is left behind sleeping while everyone else begins
the journey to the south. Awaking, he meets Manny, a mammoth who travels
to the north, and decides to follow him. When a humans camp is attacked by
tigers, a woman takes her baby and jumps on a river. Before she drowns,
the baby is rescued by Manny and Sid. The two animals decide to search
for the father and return the baby to him. Diego, one of the tigers that attacked
the humans, comes also claiming the baby.