In the previous novel (Tarzan the Untamed), during the early days of World War I, Tarzan discovered that his wife Jane was not killed in a fire set by German troops, but was in fact alive. In this novel two months have gone by and Tarzan is continuing to search for Jane. He has tracked her to a hidden valley called Pal-ul-don, which means "Land of Men." In Pal-ul-don Tarzan finds a real Jurassic Park filled with dinosaurs, notably the savage Triceratops-like Gryfs, which unlike their prehistoric counterparts are carnivorous.