Saved by the Siren from Hell

Marina is the only daughter by blood of House Ford, named head of the house and set to marry Derek. At her awakening ceremony the holy coral crown shatters. The court reads it as proof of a forbidden Medusa bloodline. Derek refuses her with one line: "I can't marry a cursed monster." By the ancient laws of the Coral Court, her father condemns her to the Abyssal Purgatory. Tara, the adopted daughter, had swapped Marina's sealing necklace for a replica.

In the Abyssal Purgatory, Marina meets Caspian, a chained prisoner and the last survivor of a fallen royal line, held for years by his uncle as a living test subject for forbidden magic. He burns from something inside him and warns her to stay away. She does not. Her Medusa blood breaks his curse; his warmth shields her from the freezing currents. Before Caspian leaves the purgatory to save his kin, they sleep together.

Marina gives birth to twins alone in that place. The sea scatters the two children. She escapes with her younger daughter Luna. Her older daughter Maya is raised by Caspian. By the time Marina gets out, her face has changed beyond recognition. For five years, she and Luna live quietly as ordinary people. Then Coral Court warships raid the coast. Marina sings, the fleet is routed, and the siren clan recognizes her as their queen.

Later, at a council of the deep-sea clans, Marina returns for vengeance. She exposes Coral Court warships that slaughtered a fishing village. Caspian, now the Abyss Lord, rules that the Coral Court must withdraw, pay tenfold compensation, send the officers to the Abyssal Purgatory, and lose its voting rights. Marina then demands the return of a siren sacred relic: the necklace Tara wears. Tara removes it. The siren signal is on the back. Marina takes it and names herself.

Caspian has spent years searching for a lead. He does not recognize Marina. Caspian wants to know what blood runs through the Siren Queen's daughter. Luna has begun to petrify; she has a month before the coral reaches her heart. Coral Court ships abduct Luna as a diversion. Caspian appears and takes the child, because her blood may save Maya.

Marina confronts Tara. Tara throws Derek in her face: he threw away the wedding ring and chose her. Marina leaves him to her. Tara claims the holy coral rejected Marina to the end. Marina answers that someone else would have taken her place with or without her. Tara then reveals that Caspian took Luna because her blood can save Maya, and by now she is probably drained dry. Marina promises Tara will return everything she stole, and next time her life is forfeit.

The truth behind the shattered crown unravels. The schemes come to light. The misunderstandings clear. Marina and Caspian join forces and destroy their enemies. Marina claims her throne as the Coral Court's rightful matriarch, settles every old score, marries Caspian, and walks into the ocean's morning light with their family of four.