The ocean is calling... With the return of the Shadowling, Astrid, Jonas and Gwen find themselves summoned by the Queen herself. They are assigned a crucial task: to retrieve an ancient weapon that the Bloom Bloods hope can stop the rising evil once and for all. But as Gwen and the twins embark on their journey, the goal of this mission leaves Gwen uneasy. And they all soon learn that the sea is full of wild and untameable magic – magic that could reveal answers Astrid and Jonas have been searching for their whole lives. With a rag-tag crew and the fate of the world at stake, who can be trusted? And what terrible things might be waiting for them in the deep?