Kevin Vance has everything—a billion-dollar legacy, a penthouse in the sky, and a marriage contract to the most powerful woman in the city. But he’s drowning.

When a freak storm capsizes his boat, he’s saved by something that shouldn't exist: a girl with reef-colored eyes and a voice like the tide. Undine. To Kevin, she is freedom. To the world of Aegis Marine Corp, she is a liability to be removed.

In a desperate bid to save her home, Kevin signs a contract that betrays their secret vow. But you cannot negotiate with the Deep. As an ancient, hypnotic law takes hold of Undine’s soul, she is transformed from a lover into an executioner.

The wedding of the century is about to become a funeral. Because when the Ocean comes to collect its debt, it doesn't want money. It wants a soul for a soul.

"I didn't want to come for you, Kevin. But the tide is high, and it's calling for what belongs to it."