Poseidon has fallen. The world won't be far behind. Unless she can stop the rising darkness.

The world beneath the waves is in chaos. Without Poseidon to hold it at bay, Dark Water is slowly spreading, devouring anything it touches. Even the mighty King Manta has given up hope.

But his daughter hasn't.

Rhea, the siren princess of Aquarius, will do anything to save her world. Even if it means hunting down the mythical Medusa—and partnering with a notorious pirate captain.

Blackheart Kai has more dangerous secrets than Rhea can fathom. He'd rather kill her than help her save her people. She knows he can't be trusted.

But knowing that doesn't stop her from needing him . . . or wanting him.

With the survival of the seven seas hanging in the balance, can Rhea and Kai overcome their hatred and work together when it matters most? Or are they destined to share Poseidon's dark fate?