An "enchanting" (Caroline Kepnes, author of You) "fairy-tale-inflected thriller" (The New Yorker) about two sisters who encounter a captivating yet possibly dangerous underworld cult that challenges their perception of reality.

Rose has come a long way. Raised--and often neglected--by a wayward mother in New York City's chaotic bohemia, she has finally built the life she's always wanted: a good job at a self-help startup, a clean apartment, an engagement to a stable if self-satisfied tech CEO who shares her faith in human potential, hard work, and the sacrifice of childish dreams.

Rose's sister Cecilia, on the other hand, never grew up. Irresponsible and impetuous, prone to jetting off to a European monastery one month and a falcon rescue the next, Cecilia has spent her life in pursuit of fairy-tale narratives of transcendence and true love--grand ideas Rose knows never work out in the real world. When Cecilia declares she's come home to New York for good, following the ending of a whirlwind marriage, Rose hopes Cecilia might find a way to be ready to face adulthood: compromises and all.

But then Cecilia gets involved with the Avalon: a cabaret troupe--one that appears only at night on a boat that travels New York's waterways--and soon vanishes. The only way Rose can find Cecilia is by tracking down Avalon herself.

But as Rose gets closer to solving the mystery of what happened to her sister, the Avalon works its magic on her, too. And the deeper she goes into the Avalon's underworld, the more she begins to question everything she knows about her own life, and whether she's willing to leave the real world behind.