Arrangements have been made for Smudge to stay with Mr and Mrs Butt and their obnoxious son Billy, whilst his parents go on holiday. Billy Butt is a naughty, greedy bully and a food worshipper. The boys hate each other. On a day out, Billy runs off to explore, and Smudge chases after him into a dark forest where they get hopelessly lost. It is there where they fall into the evil hands of Madge and Reggie Stinkhorn, who lure them into their home with the promise of tasty treats. It is also there where the boys are trapped and made to work as slaves in an underground factory, run by two nasty henchmen, Limpitt and Muscles. They eventually discover a sinister trade involving monstrous creatures, where secrets lurk around every corner. They must escape to tell the world. 'What they encountered next was something too hideous to mention, but it will be mentioned, because it was hideously fascinating.'