A plague of locusts strikes the Great Valley, decimating the plants and forcing the dinosaurs to migrate in search of food. When the adults in the herd begin fighting over the scarce resources, young Littlefoot and his friends Petrie, Cera, Ducky and Spike split off from the main group, becoming stranded on an island after their path was destroyed by a tsunami. As they search for a way off the island, they encounter an old acquaintance who may become friend or foe.