The God Beneath the Sea is divided into three parts. Part one begins with the image of the infant Hephaestus plummeting from Olympus to the ocean. Thetis saves the baby and takes him to the grotto she shares with Eurynome. They raise the baby, telling him stories of Greek myths and giving him a hammer and anvil to play with. Part one concludes with Hermes inviting Hephaestus back to Olympus at Hera's bequest, and Hephaestus claiming Aphrodite for his wife. Part two tells the myths of Prometheus and Pandora, and part three tells various myths of gods interacting with mortals. The novel concludes with the Olympians unsuccessfully attempting to overthrow Zeus, and Hephaestus returning to Olympus from Lemnos, having been cast down from Olympus for a second time after reproaching Zeus.