Secrets of the Deep (The Gryphon Chronicles, Book 5) - E. G. Foley

Some lost treasures were never meant to be found... With the Dark Druids after him and a magical war brewing, thirteen-year-old Jake Everton must lie low for a while, so Aunt Ramona, the Elder witch, takes him and the gang on a long beach holiday out of harm's way - supposedly. But, sure enough, Jake plunges into trouble once again when he meets a feisty royal mermaid on the run.

Crown Princess Sapphira, the adventurous daughter of King Nereus, recently ventured to the edge of the Calypso Deep and stumbled upon a powerful artifact from ancient Atlantis. But the mysterious orb holds deadlier secrets than she ever suspected, and soon, every power-mad tyrant in the Seven Seas wants it - especially the dread, undead pirate king, Captain Davy Jones. When the legendary Lord of the Locker invades her father's kingdom, demanding the orb and taking her little sister hostage in exchange, Sapphira turns to her new friends, Jake and company, to help her rescue Princess Lil and stop Davy Jones from using the artifact's powers to expand his watery territory by covering the earth in a second Noah's Flood! (450 pages / 175,691 words)