A new prophecy leads to a dangerous quest. When Percy receives an urgent distress call from Grover, he immediately prepares for battle. He knows he'll need his powerful demigod allies, Annabeth and Thalia, at his side; his trusty bronze sword, Riptide; and...a ride from his mom. The demigods race to the rescue, only to find that Grover has made an important discovery: two new powerful half-bloods, whose parentage is unknown. But that's not all that awaits them.