After wondering for some time, Sid, the sloth, Manny the mammoth and Diego, the sabre-toothed tiger are still one pretty weird and awesome pack. They are sticking together no matter what and it is working out pretty good for them. As they wonder, Manny starts thinking about starting a new family, but the only problem is, they haven't spotted a mammoth in quite a while. At one point, he starts thinking that he may be the last mammoth alive. Suddenly, this weird trio comes across Ellie. She looks like a mammoth, but she is more than convinced that she is a possum. How is that? Well, as she tells her story, we get to find out that she was raised by possums and that she has learned to live like them. She also has two brothers- Crash and Eddie, who are real possums, not like her. They are anything but calm- loud, funny, crazy, capable of any kind of stupidity. It is a hard to convince Ellie that she may be a female mammoth, and that she may be the last one of her kind as well. Besides that, while everyone is enjoying in a warmer climate, guys manage to find out that if the glaciers melt down, the world will be covered with water. And their only chance is to get to the other valley.