Manny, Sid, and Diego are currently living in a large valley surrounded by an enormously high ice wall on all sides. When a water park begins to form, the trio discovers that the ice wall is actually a wall that is barely holding a massive body of water that could flood the valley to nearly a mile underwater. A vulture tells them that there is a boat at the other end of the valley that may save them all, but they only have 3 days to make it or die. Manny is having trouble facing the fact that he may be the last mammoth left. Along the way, they meet Ellie, a mammoth who thinks she is a possum, and her possum brothers Crash and Eddie. As they begin to travel together, Manny learns, with help from Diego and Sid, that having this new mammoth with them, may not be as bad as Manny makes it out to be while they try to escape the oncoming and continually threatening flood. During their journey, Scrat the sabre-toothed squirrel has his own hilarious adventures that eventually leads to something else entirely.