Nadia and her cat Orains pilot the Lilly Princess around the world in search of sunken magical treasure. She's got a lead on the sunken wreck of the Astrea and its magical cargo. A magical storm conjured by the Samurai, a group of mages with designs of their own on the treasure, pushes them off course. What could have scuttled the entire mission turns fortuitous when they discover the mystical treasure of Neptune's Cat. And once Orains puts on one of the collars, things may never be the same again.