Poseidon's Academy and the Olympian Mysteries (Book 4), Paperback

Hailey's worst fear has come true: the gods have returned from the dead. Before anyone can call on her to fight them, Hailey flees to Poseidon's Island. She doesn't care that there's a prophecy that says a Zeus is the only one capable of defeating the gods; she has no intention of entering the battle that's about to be waged... That is until the gods begin enslaving the human population and burning entire cities to ash. As much as she wants to hide away, Hailey can't stand by and watch people die. She teams up with her friends and enters into the chaos. But the gods aren't working alone. A cult known as the Olympian Mysteries is protecting them, and they'll stop at nothing to keep the gods in power-especially if it means killing Hailey to put an end to the prophecy once and for all.