When Alfie Mandeville's insomnia threatens to embarrass his wealthy family he is sent to Scarbrook House, a sanatorium for wealthy children. Troubled by the eerie atmosphere and skittish patients, Alfie's condition gets worse, not better. He falls under the spell of the charismatic and cruel William Travers, who seems to delight in bullying the other patients. A mysterious sighting by the water tower in the woods stirs up turbulent memories of Alfie's time in India. And as he lies awake one night, Alfie is haunted by visions of a strange creature moving through the darkness at the edge of the patients' beds. Are his tired eyes playing tricks on him, or is he starting to lose his mind? When Alfie learns that the creatures are hunting a demon escaped from the depths of Hell-and that the only protection against them is to be asleep-suddenly insomnia becomes the most dangerous condition of all...