Jason Gridley is experimenting with a new radio wave when he gets a message. His invention has made contact with Pellucidar and Abner Perry. Perry recounts the story of Tanar.
The Empire of Pellucidar has grown and prospered since the overthrow of the Mahars. A new enemy comes to the shores of the empire. Korsars, descended from eleventh century Spanish pirates attack. They are repulsed but at great cost. Tanar the son of Ghak the king of Sari has been captured. The Korsars want to get the secret of the empires superior gunpower and bring Tanar to their capital.
Along the way a storm shipwrecks Tanar with Stellara the daughter of the Korsar leader. Through a series of adventures the two fall in love are recaptured and taken to the Korsar city. There they are united with David Innes who was also captured. Tanar and Stellar escape after finding the north polar opening to the surface world. Emperor Innes is still a prisoner in the dungeons of the Korsars. The book ends with Jason deciding to mount a rescue mission.
This is probably one of my favorite stories that Burroughs wrote. Tanar and Stellara are a classic romantic tales. It also sets up the only crossover that Burroughs did Tarzan at the Earth’s Core.