In the previous novel Tarzan and Jane's son, Jack Clayton, a.k.a. Korak, had come into his own. In this novel Tarzan returns to Opar, the source of the gold where a lost colony of fabled Atlantis is located. However, while Atlantis itself sank beneath the waves thousands of years ago, the workers of Opar have continued to mine all of the gold, which means there is a rather huge stockpile. Tarzan follows a greedy Belgian and an Arab into the jungle, where this criminal pair manages to stumble upon this lost city. John Clayton loses his memory as an after effect of a fight, and La, the high priestess who was the servant of the Flaming god of Opar, and who is also very beautiful, takes advantage of his amnesia. She had fallen in lust with the ape man during their first encounter. But while his amnesia opens the door for La's lustful advances, her high priests are not going to allow Tarzan to escape their sacrificial knives this time. In the meanwhile, Jane is in trouble and wonders what is keeping her husband from once again coming to her rescue.