The descendants of the Little Mermaid face deadly magic, shifting alliances, and the dangers of forbidden love in this final installment of the Mer Chronicles. 

Lia can't wait for her parents' coronation. Now living in the sparkling palace beneath the waves, she sneaks off to Malibu whenever possible to see Clay. Tucked away in an abandoned seaside mansion, Lia and Clay devise a plan to ensure they can stay together forever. But when an old enemy resurfaces, and Lia is restricted to the palace for the safety of all Merkind, she and Clay are ripped apart once more. 

She fears not only for Clay, but for her best friend Caspian, who seems to be swimming down a dangerous path. He has invited the conniving Melusine to the coronation ball, convinced she's capable of change. And no matter how hard Lia fights it, showing up on Caspian's arm is just the start of Melusine's insidious return to her life. With threats Below growing more ominous by the day and a powerful ancient ritual looming, soon the two girls can't escape each other. 

As their fates grow increasingly intertwined, Melusine might be the only one who can help Lia find the answers she desperately needs to save everyone she loves and to achieve her happily-ever-after. But can Lia trust her?