The eight book in the series picks up as Tarzan searches for Jane. He tracks the German officer that took her to the land of Pal-ul-don. This land is a lost land inhabited by men with tails. Tarzan befriends a Waz-don and Ho-don, the black and white inhabitants of this valley. The Waz-don live in caves while the Ho-don are city dwellers and ride Gryfs or Triceratops.
Tarzan finds his wife captive in the Ho-don city and being used as a pawn in a power struggle between the king and high priest. The Ho-don religion believes that their god is tailless. The king wants to use Jane and Tarzan as emissaries of their god to increase his power. The high priest denounces them as false gods.
Eventually the timely intervention of their son Korak who has also tracked Jane saves the day. An ally of the ape-man is placed on the throne the Tarzan and his family are allowed go back home.
This was an excellent book. I loved the strange races and creatures that inhabit this mythical land. Burroughs created an intricate and believable society. He was at his best in imagining strange civilizations and firmly established the success of this series.