Im Dschungel von Kun-Kau-Peh

From the back of the book (translated):
For centuries the tribe of the Yakosh-Dej is living in the shadowy depths of the rain forest. The forest people go hunting, raise their children and celebrate their ritual feasts like their fathers and forefathers did. So they could live in peace for many years, but the tribe has a secret: It knows a herb that lends marvelous power. When an alchemist gains knowledge of this plant the peaceful life of the forest people is over: Lust for power and lucre threaten to destroy the tribe if there are no upright heroes to be found who put an end to it...