In the treacherous waters surrounding Kirkrell, sailors hunting magic whales live in fear of the finfolk—bloodthirsty sea fae who sink ships and curse bloodlines. Nineteen-year-old Annie, as heir to the city's preeminent whaling company is determined to carry on her parents' lifework. But she keeps a secret from everyone: she's cursed to transform into a monster, with scales spreading up her arms and claws growing from her fingertips.

Her fiancé, August, offers comfort, but their love falls apart when Annie discovers his plan to take over the company. Desperate, Annie makes a deal with Silas Price, a young captain rumored to be half finfolk. He claims he knows how to break the curse—but only if Annie promises to stop the practice of whaling forever.

As Annie, August, and Silas sail north, Annie—wrestling with her family's legacy, the threat of the finfolk, and August's ambitions—is increasingly forced to put her trust in Silas. Yet Silas has secrets of his own, and they might be the most dangerous of all.