Set on a world where a giant tree called Kaena rises 100 miles above the surface, this is a tale of adventure that occurs when a young woman, Kaena (Dunst), leaves her village hoping to discover why the tree's sap is disappearing. Coming down past the clouds, she meets the Selenites, a race (led by a Queen voiced by Huston) that is also trying to keep the tree from dying, although by enslaving another race. Can Kaena discover why the tree that gives them all life is imperiled?