With the help of Castor and Pollux, seventeen-year-old Gen tries to fulfill her end of a bargain with the Olympian Empresses and bring them the legendary golden apples of Hesperides and the monstrous Cerberus while also avoiding war with neighboring Elysium.
Demon is getting used to his role as the official Beast Keeper to the gods on Mount Olympus. the gods are getting used to him, too - until Helios and Poseidon decide to involve him in a feud! The two gods are planning a race to see which of their steeds are the fastest. Both the vengeful gods have requested Demon's help, but he can choose only one.
Having proven himself capable of caring for the mythical creatures that dwell on Olympus, eleven-year-old Demon is summoned by the great god Hades to the Underworld to tend to Cerberus, the three-headed dog Guardian of the Underworld, which has been beaten by Demon's nemesis, Heracles.
Retells the story of the final, and most difficult, labor of Hercules, known as Heracles in Greek mythology, in which he must go to Underworld and bring back the three-headed dog, Cerberus.