Tarzan the Invincible (Tarzan, #14)

Tarzan, his monkey friend Nkima, and Chief Muviro and his faithful Waziri warriors prevent Soviet communists from looting the lost city of Opar. The story also prominently features Tarzan's lion ally Jad-bal-ja.

The novel was originally serialized in the magazine Blue Book from October, 1930 through April, 1931 as Tarzan, Guard of the Jungle.