Littlefoot befriends with a mysterious, fun-loving dolphin-like creature named Mo, who is trapped in "new water" caused by heavy rain. The gang then goes on an adventure to the "big water" to bring Mo home.
This time, while building a hideaway in their new home of the Great Valley, Littlefoot and the gang rescue a mysterious egg from two scheming egg-nappers and make a starling surprise - and new friend - when the egg hatches.
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.