Once there, she is plagued by clairvoyant visions as she looks into the magical secrets of the school with her three friends Felicity Worthington, Pippa Cross, and Ann Bradshaw.

Gemma Doyle, the series' protagonist, is forced to leave India after the death of her mother to attend a private boarding school in London.

With her mother dead and her father's addiction to laudanum growing stronger, Gemma's family ships her off to a finishing school in London: Spence Academy for Young Ladies.

There, she finds a diary written 25 years earlier by a 16-year-old girl named Mary Dowd who also attended Spence Academy and seemed to suffer from the same visions as Gemma, along with her friend, Sarah Rees-Toome.

Through this diary, Gemma learns of an ancient group of powerful women called the Order and becomes convinced that her visions are linked to it.

Members of the Order could open a door between the human world and other realms, help spirits cross over into the afterlife, and also possessed the powers of prophecy, clairvoyance, and what was considered the greatest force of all, the ability to weave illusions.

Gemma, Felicity, Pippa, and Ann decide to create their own Order in the caves to escape from the monotonous lives that they are expected to lead.

Kirkus Reviews said the book was "Gothic touched by modern conceptions of adolescence, shivery with both passion and terror.