Eunice lives her life by three simple rules: One, always refer to Cinderella as family. Two, never let Cinderella gain access to rats or mice. Three, never look upon Cinderella between the hours of twelve and three a.m.

Cinderella has dark and terrifying powers. As her stepsister, Eunice is expected to care for her and keep the family's secret. For years, Eunice has faithfully done so. Her childhood flew by in a blur of nightmares, tears, and near-misses with the monster living in the cellar. But when she befriends the handsome Prince Credence and secures an invitation to the ball, Eunice is determined to break free.

When her younger sister, Hortense, steps up to care for Cinderella, Eunice grabs her chance to dance the night away—until Cinderella escapes. With her eldritch powers, Cinderella attends the ball and sweeps Prince Credence off his feet, leaving behind a trail of carnage and destruction as well as a single green glass slipper.

With Cinderella unleashed, Eunice must determine how much of herself she is willing to sacrifice in order to stop Cinderella.