The colt of the clouds
(Book)

Ever since Pippa and her beloved horse, Zephyr, were banished from the slopes of Mount Olympus, they've tried to adjust to living a normal life on the ground. But when Pippa rescues a lost winged colt, she knows she must take him to the land of the gods and goddesses, where he belongs--even though she's been warned never to return. Up on Mount Olympus, however, disaster awaits. The gods and goddesses are at war, and all of the winged horses have disappeared. With the help of Hero, the not-so-heroic descendant of Hercules, Pippa takes on a task few mortals would dare: to find the winged horses and end the war.