In a frozen prehistoric world, a mismatched trio of mammals find themselves unexpectedly united by a common cause. Sid, a talkative and slightly annoying sloth, has been left behind by his family and is looking for protection. Manfred, or Manny, is a grumpy and solitary woolly mammoth moving against the migrating herds to follow his own path. Diego, a sly and ambitious saber-toothed tiger, comes from a pack with a more sinister agenda. Their lives intersect when they come across a human baby that has been separated from its tribe.

The unlikely group decides to return the infant to its human family, embarking on an arduous journey fraught with danger and challenges. As they traverse the shifting landscapes of the ice age, they must contend with environmental hazards, predatory creatures, and their own interpersonal conflicts. Despite the friction among them, the trio begins to form a bond, shaped by their shared experiences and the need to rely on each other for survival.