Wholesale Olympus at War by Kate O'Hearn

[Aladdin] Emily and her winged horse face a war of Olympic proportions in this second book of an adventurous series. Emily, newly recognized as the Flame, is living in Jupiter’s palace on Mt. Olympus. Her friends, Joel, Paelen, and—of course—Pegasus, are there as well. The only person missing is Emily’s father, who is still being held prisoner by the CRU back in the human world. Emily wants to go find him, but Jupiter won’t allow her to leave. However, Emily does have access to a winged horse… Determined to rescue her father, Emily and her friends make plans to sneak away from Olympus and back to New York. Then Cupid, Emily’s sort-of crush, decides to come along as well. It will be hard enough to hide a winged horse from the prying eyes of the CRU, but a winged boy as well? And when the gruesome Nirads begin a new invasion, old grudges are unearthed, new enemies are discovered, and Emily and her friends become entangled in a conflict more dangerous than they ever anticipated.