Evie and Mia meet on a train on their way to St.Agatha’s Boarding School for Girls. When they are dropped off at a disused railway station in the middle of nowhere with no one to meet them, they trek through the pelting rain and darkness for miles until they find a sign to St.Agatha’s which points to an unlikely overgrown track leading up a mountain path.
The school is a foreboding place, set high up on a mountain, surrounded by a sea of mist, and overlooking a loch. Coming face to face with the grotesque caretaker, Mandrake, does nothing to allay their fears. What is the significance of the strange rings worn by Miss Blackthorn, the head teacher? Why does Evie not receive any post from her parents?
Evie and Mia stumble across a forgotten burial chamber where the skeleton of Sister Beatrice lies, clutching a note. The note details a curse which she has laid on the land. Locked in the chamber as a punishment, the girls uncover an old book within which is the antidote to the curse, but it is hidden in code.
The girls then make a terrible discovery. Are they daring and innovative enough to plan a scheme that will foil evil and get them out of a dangerous situation?