Set during the Ice Age, a sabertooth tiger, a sloth, and a wooly mammoth find a lost human infant, and they try to return him to his tribe.

A star-studded cast provides the voices for the prehistoric creatures in this computer-animated feature set 20,000 years ago as the Ice Age approaches. Seemingly anti-social Manny, a woolly mammoth (voiced by Ray Romano), acts as if he just wants to be left alone. When he meets Sid (voiced by John Leguizamo), a sloth, the two become unlikely traveling companions. The plot thickens when the duo finds a human infant and decides to try to return the child to its "herd". Manny slowly but surely reveals his heart of gold, while Sid continues to provide comic relief. Diego (voiced by Denis Leary), a saber-tooth tiger with ulterior motives, soon joins them in their search for the humans. Ultimately, this group of misfits becomes its own herd, learning about friendship and loyalty as they brave snow, ice, freezing temperatures, predators, hail, and even boiling lava pits. All the while, a saber-tooth squirrel, Scrat, provides comic relief as he valiantly struggles with an acorn. A well-written, humorous script and endearing characters mesh well with the state-of-the-art technology and effects. Other stars lending their voices to the feature include Goran Visnjic, Jack Black, and Jane Krakowski.