The Nightmare Game by Gillian Cross
Hope has gone. Warren saw her being taken from her prison under their father's house but was too scared to intervene. Now he wishes he'd been brave enough to stop Rob, Emma, and Tom kidnapping her. His father is furious, but it's the behaviour of Warren's normally-cowed mother that's most frightening. For years, she has known her daughter was safe in the hole under the conservatory. But now Hope is out in the world, and anything could happen to her. Mum has to get her back. She's going to start by doing something terrible to Hope's kidnappers, and Warren must help. Rob Tom and Emma have other things on their mind. When they took Hope, it was to save her. But now Hope has disappeared. Could she somehow have escaped to the world of miniature people where Rob's friend Lorn is fighting for survival? Just when the three friends need to be closest, Emma disappears and Tom starts acting really weirdly. Rob is sure the man with blue eyes has something to do with it. He's seen him in town again. If he dares to confront him, will he be able to save his pals? And if he's wrong, what price will they all end up paying?