The ocean is calling... With the return of the evil Shadowling, Astrid, Jonas, and Gwen are faced with a new task: by order of the Queen, they are sent on a top-secret journey across the sea to retrieve ancient weapons that the Bloom Bloods hope can stop the Shadowling once and for all. Gwen and the twins set off, but it's not all plain sailing. When their ship is jeopardised, they must turn to an unlikely source for help, and worst of all, a certain royal shipmate keeps pestering them. They will soon learn that the sea is full of wild and untameable magic - magic that could reveal answers the twins have been searching for their whole lives. With their rag-tag crew and the fate of the world at stake, who can they trust? And what terrible things might be waiting for them in the deep?