A message by Sir Thornberry lures both the Gummis and Igthorn back to Ursalia, where a new band of Gummis, the Barbics, have taken refuge. The new tenants, however, are mostly a rather unsociable bunch with a deep hatred for all humans. They seek the ultimate weapon in Ursalia to get revenge against the humans, and as it so happens, this weapon is close to falling into Igthorn's hands.

Cubbi accidentally wrecks Ursalia's water reservoir, leaving the ancient metropolis short of its most important commodity. While Gruffi, Ursa and Sir Thornberry keep bickering whilst following an ancient aqueduct to find out why the water flow has stopped, Gritty and Cubbi try to lasso and train a few ramas (an amalgam of ram and lama) to fetch water from the not-so-nearest river. But then Gritty tries to get revenge on a group of mountain shepherds for human crimes against the ancient Gummi Bears, and Cubbi has a hard time trying to persuade him otherwise.

Igthorn and his ogres have destroyed Gummi Glen, captured Dunwyn Kingdom and its citizens, and are keeping Grammi and Tummi held in Drekmore. Now Cavin and the remaining Gummies, with the help of the Barbics, must save them all while Zummi retrieves the Great Book and warn the Great Gummies to turn back.