Ethan, Lily, Saxon, and Roana have cracked the code, only to find that the Moon Pearl is being sent by ship to the land of the invaders. The four children must give chase to save the precious stone! The fisherfolk can help. So can Saxon's mysterious acquaintance, Fox, a smuggler who will do anything for a pouch full of Roana's gold. But the sea is far more dangerous than the land. There are sea monsters and wild storms—not to mention the deadly warship they are chasing. Will Fox's stealthy black sloop, the Owl, carry them to safety, or will the Moon Pearl remain in the hands of their enemy?