A brand-new underwater adventure from the author of the long-running Beast Quest series!Max's home, the floating city of Aquora, is attacked by Cephelox the Cyber Squid and his father is carried away by the Robobeast. Max and his robodog, Rivet, set off on a rescue mission. Along the way, they meet Lia, a princess of an ancient race of Merryns who live underwater. The Merryn's magic powers are fading because the evil Professor has stolen four pieces of a skull that is the source of their abilities. The Professor has four dangerous sea creatures guarding these pieces. It is up to Max and Lia to retrieve these items and save Max's father before it's too late.