Her father is dead thanks to her wretched, siren step-mother, and as a fully transformed mermaid, she's a prisoner in the Undersea. But turning to sea-foam is the last of her worries when she realizes that her battle with Melody has caused her to inherit the title of Reigning Queen. Now, with her heart magic twice as valuable, she must tread carefully in her attempts to adjust to mermaid life and reclaim her best friend's soul from the treacherous Sea of Souls. But Coral soon finds herself in trouble once more, and she realizes that if she's going to accomplish any of her goals, she may need the help of the very siren step-mother who destroyed her life in the first place... As tension builds between the kingdoms, Lysander and Coral know they must present a united front against Eugene's forces-that their bond is the only thing maintaining Coral's Reigning Queen status, and without it, she won't survive the Sea of Souls, nor have enough power to dethrone Eugene. But despite Lysander's attempts to navigate life as a fully moral being, he can't help feeling like his relationship with Coral is crumbling. Especially now that Coral's twin has arrived in Veranis, proving to be everything Coral is not. And though he doesn't want to admit it, he's beginning to think that he picked the wrong sister...