"Berkeley and her best friend, Garth, live on an old cruise ship, scavenging for supplies from the drowned cities left behind on the ocean floor after the sea swallowed up all the land. They think they've seen every kind of aquatic creature, but they never expected to find sea monsters... After awakening a Hydra, Berkeley and Garth are sent to live on a submarine, where they study and hunt sea monsters. But the Hydra wants revenge on their home ship--and...

While on a mission aboard the The Emperor of the Seas, Ben Ripley faces off against his arch enemy, Murray Hill, on the high seas and quickly finds himself in hot water as things take a dangerous turn.

The Kingdom keepers and their friends discover that Maleficent and the Overtakers are plotting a catastrophic event that could have repercussions far beyond the world of Disney unless they solve a puzzle that is revealed during the Disney Cruise Line's inaugural passage through the Panama Canal.