Best friends Karlheinz Indergarten and Leopold Croak clash in an epic, imaginary battle waged in the branches of an enormous, ancient oak tree. But when lightning strikes young Leopold, he loses his imagination, and with it, his sense of right and wrong. The damaged boy grows to adulthood, treading a sinister path of industrial conquest. And Leopold’s thirst for power soon threatens the tree, the village, and worst of all, the children within.

But humble Karl discovers a gift for clockwork—the magic of gears and cogs—and assembles a mechanical army to fight back. Joined by the children themselves, Karl endeavors to save the village, the ancient oak, and maybe—just maybe—something more besides.