When Littlefoot and the other kids try to find out why the fast-water stopped flowing, they run into their old friend Mo! Littlefoot, Mo and the other kids work together to get the water flowing again. Chomper puts Cera in her place when he proves that his little arms aren't just okay, they're good enough to save the day!

When Doc, an older longneck that Littlefoot believes to be the legendary Lone Dinosaur, arrives unexpectedly, the kids are convinced he's there to drive Chomper but of the Great Valley. While Littlefoot tries to discover Doc's true intentions, Cera leads the other kids on a wacky journey in an attempt to hide the panic-stricken Chomper.