Zeus and the Skeleton Army (Heroes in Training #18) by Tracey West, Craig Phillips (Illustrator)

Zeus and his fellow gods-in-training face a new challenge in the underworld when they attempt to capture Cerberus—the three-headed guardian and cherished pet of Zeus’s brother Hades. But they find themselves up against even more than they anticipated when they have to face off against Melinoe and her skeletal minions.