The novel is about twins Matt and Emily ("Em") Calder who share an ability that allows them to make artwork come to life, due to their powerful imaginations.

Their ability is sought after by antagonists who wish to use it in order to breach Hollow Earth—a realm in which all demons and monsters are trapped.

Other locations which feature in the novel include Glasgow's Kelvingrove Art Gallery and Museum and the "Pencil" Monument near Largs.

[2] Since Art and artwork is an important theme in the novel, many of the paintings mentioned are based on or inspired by real-life works of art from artists such as Georges Seurat, William Blake, Vincent van Gogh, Henry Fuseli and Salvador Dalí.

[4] The book has been described by Sarah Swain of The Herald as a Scottish-style version of Harry Potter.