In the previous volume, the Lord of the Jungle discovered the burnt corpse of his wife, Jane, after a visit to his African home by German soldiers. (One suspects that Burroughs never did like Jane; this sort of thing happened to her a lot.) In this volume, Tarzan learns that Jane was not murdered by the Germans but kidnaped -- and sets off in pursuit. As the novel begins, Tarzan has spent two months tracking his mate to Pal-ul-don (-Land of Men-), a hidden valley in Zaire, where he finds a land dinosaurs and men even stranger -- humanoids with tails. Ta-den is a hairless, white-skinned, Ho-don warrior; O-mat is a hairy, black skinned, Waz-don, chief of the tribe of Kor-ul-ja. In this new world Tarzan becomes a captive -- but he impresses his captors so well that they name him Tarzan-Jad-Guru (-Tarzan the Terrible-). Meanwhile, a second visitor has come to Pal-ul-don -- wearing only a loin cloth and carrying an Enfield rifle along and a long knife. Pal-ul-don is where Jane is being held captive, of course. . . .