The year is 1915 and sixteen-year-old Eliza Williams has just arrived at the Billings School for Girls, the sister school of Easton Academy, founded to turn girls into dutiful wives. Eliza's parents expect her to learn the qualities needed to be a graceful and obedient wife, but Eliza has a dangerous secret… she's a witch!

After finding a dusty, leather-bound spell book, Eliza forms a secret coven with eleven other Billings girls, disguising their gatherings as a literary society to keep their teachers from discovering the truth. Bonded in sisterhood, they cast spells - cursing the headmistress, giving blisters to boys with wandering hands and conjuring beautiful dresses out of rags. The girls taste freedom and power for the first time, but what starts out as innocent fun turns into something more sinister when one of the spells has an unexpected - and deadly - consequence. Eliza realises that magic could bring her everything she's ever wanted… but it could also destroy everything she holds dear. But is it too late to stop what she's started?