Isla Maris overhears her fiancé plot her death for shares and insurance. Her own brother throws her into the sea. In the abyss, an ancient shape rises. She grabs a rusted sword, awakens a Sea God imprisoned a century. He calls her "Pelagia," the queen who betrayed him. He vows revenge, but when she cries, his curse bleeds, and when she whispers a forgotten name, he holds her hand. She returns to the surface with his power, discovering her death was no accident: her family runs an illegal deep-sea mining operation, trafficking murdered merfolk. She will drag them to court, or the ocean will. But the world discovers her Sea God, demands she hand him over. Now she must choose: her humanity, or the god who swore to make her suffer, yet may be the only one willing to protect her.
