When a sudden shortage of water threatens all life in the great valley, The gang of young dinosaur must cooperate with a group of bullies to make a risky journey outside the valley and find the cause.

Grandpa tells Littlefoot about their mythical hero called the Lone Dinosaur. Sarah gets two little lively cousins to take care of. Later, the kids accidentally chip the lucky Saurus Rock, and need to fix it before the bad luck hits.