When 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. But since she's spent the last couple of years on land, Lily's not sure she has the fins to lead a kingdom. Even her maddeningly pretentious cousin Dosinia seems to know more about ruling than she does. But Lily has to dive in deep to keep her promise to Tellin, her mer bond in name only, who tells her his 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. 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. It feels as if the pair is up against a solid tsunami wave! In this third installment in the series that began with Forgive My Fins and Fins Are Forever, Lily will have to find a way to balance safety and justice for the mer people and for the humans she loves.