With the collapse of large glaciers, the Ice Age has finally become history! And our main characters begin to start their own families. But Sid the squirrel is always Sid the squirrel, whenever he gets involved, chaos ensues! He actually got a few dinosaur eggs! And now, a giant dinosaur appeared out of nowhere, and Sid was immediately captured. For their friend who had gone through thick and thin with them, the other three members of the "gang" said goodbye to their wives and children, and set off again on a journey to rescue Sid. But this time, the trouble far exceeds their imagination. It turns out that Sid was taken into a magical underground world, isolated from the outside world, with humid air and warm climate. It blocked the biting cold winds of the Ice Age, and as a result, a large group of ferocious dinosaurs appeared before them...