Zach Applewood is an ordinary schoolboy, being raised by his father, with whom he enjoys a good relationship. His teacher, Mr Quinn, helps him to regain self-esteem, following a terrible previous year at school, with the spiteful Mrs Swann. Events begin to take a sinister turn, upon the arrival at his school of a strikingly unusual girl, with a distinct air of mystery about her - Emma Vallance. A school visit to the caves of Wookey Hole soon turns into nightmare, as strange creatures appear and attempts are made to kill Zach; or, even worse... Zach realises that there is far more to know than meets the eye about Emma Vallance, and the two teachers in charge of the visit: Mr Quinn and Mrs Swann. Zach must learn very quickly that there are far more things in this world than he ever learned at school. He encounters species that feed upon the living, without them even being aware of it: these are the shadows in the corner of the bedroom at night, the sound beneath the bed, the stranger lurking around the corner... the Unseen. Layer by layer, the new reality of Zach's world unfolds. This is the place where the dead walk; where the fabric of the Earth distorts; where monsters that suck out the psyche and feed upon intellect roam. He discovers - and has to come to terms with - his own previously untapped powers... Zach finds himself thrown into a showdown, in the very bowels of the Earth, in a disused under-sea mine; a showdown that will test the limits of his new-found power, and unlock the mystery to the recurrent nightmare that has haunted him since before he could remember.