On a geological expedition into darkest Africa, Rex Brandon encounters two explorers, Litzgor and Dorton, both suffering from malaria. Brandon administers medical aid, and upon recovering the two men relate a fantastic tale. Whilst prospecting in an unexplored region they had been driven to flee when attacked by a hostile native tribe led by a white woman with a mighty lion at her side, completely under her control. Litzgor had dropped his new invention, an electronic box—now in the hands of the mystery woman. But does she and her lion actually exist, or were they malaria-induced delusions? Brandon agrees to help Lizgor return and recover his instrument — but in learning the truth, he places his expedition in danger ...