Exploring a cave at the edge of the Great Valley, Littlefoot and his friends are trapped by a rock fall. As they try to find a way out, Spike notices they are not alone? There?s a Sharptooth sleeping in the cave! The young dinosaurs scatter and soon become lost in the Mysterious Beyond? Cera has been captured in the desert by a Scorposaurus. Spike is trapped on an island deep in the swamp by an angry Sharptooth. Ducky is hiding from a Spiderdon in the caves.
Petrie soon finds Littlefoot and the two of them set out to rescue their friends and get home.