The acclaimed author of House of Frost and Feathers returns with a sweeping, lyrical novel inspired by a mermaid folktale filled with exploration, love, adventure, and magic. A GREAT LOVE. A MYSTERIOUS KINGDOM BENEATH THE WAVES. A DEVASTATING BETRAYAL. A doomed love story created the city of Ys, it's fitting that another one would end it . . . Nolwenn is sure that her life's purpose is to defend her beloved coastal city of Ys as a lighthouse keeper. But when a dangerous, unnatural tide threatens Ys, the queen instead tasks Nolwen with collecting enough rare seasilk to shield the city from the deadly monsters who lurk deep beneath the waves. Determined to fulfill her task, Nolwenn recklessly puts her life in danger, only to be attacked by the very creatures she's trying to defend her city against. She's saved by Morvan, a member of the korrigez people, with the torso of a human and the tail of a fish. Against her will, Morvan drags her deeper into the ocean to the coral palace of Below-Ys. Although Nolwenn is terrified and homesick, Below-Ys is also strange and beautiful...as is Morvan. The more time Nolwenn spends below the surface, the less she is sure she wants to leave. As danger draws ever nearer to her homeland and Ys remains precariously unprotected, Nolwenn must decide between her heart and her home.