Ohen Lily Sanderson decided to remain Crown Princess Waterlily of the mer kingdom of Thalassinia, she knew she couldn't just coast along in the current. Since she's spent the last couple of years on land, Lily's not sure she has the fins to lead a kingdom. But she has to dive in deep to keep her promise to Tellin, whose kingdom is suffering in the changing ocean climate. Lily knows this is a seven seas–sized problem. They'll need to create some serious waves to make the mer community aware and get it to join together to make things right. Lily has to lead the way, even if that means facing one of the iciest queens in the mer kingdoms.

And just when Lily thinks her double life on land and sea can't get any more complicated, an ancient mer law might separate Lily and her human boyfriend, Quince, after all. Can they swim their way through this rough surf?