Hound of Hades (Beasts of Olympus Series #2)

Beasts of Olympus is a series of 144-page illustrated chapter books set in a magical Ancient Greece where strange things still walk the Earth. In this second book, young Demon is summoned by the great god Hades to the Underworld. His most-hated hero, Heracles, has just returned Cerberus—the three-headed dog Guardian of the Underworld—to his god master, but something is wrong with the beast . . . and only Demon can help.