From epubbooks.com:
Allan Quatermain is confronted with the legend of the Heu-Heu, a monster who eats humans, while sheltering from a thunderstorm in the Drakensberg mountains. The legend appears to be reality as Quatermain is to find out after arriving in Zululand and being summond by Zikali, a Zulu Sangoma of indeterminate age. Together with his trusted companion, Hans, Quatermain is sent on a mission by Zikali. This mission is, firstly to procure a potent herb which Zikali needs and which happens to originate from a tree in the Heu-Heu’s garden. Secondly, it is to overthrow the Heu-Heu at the behest of Issicore, a noble from the tribe Walloo, the worshipers of Heu-Heu, who has travelled to Zikali to ask for assistance.