'At that moment the kitchen door opened and something colossal came stomping out. It was about seven feet tall with green skin and tufts of black fur on the back of its ham-like hands. A long, thick tail was dragging heavily across the floor behind it. It was wearing Mum's green summer dress and white apron.' Lewis and Greg have accidentally turned their mum into a troll, and the town of St Andrews into a fantasy world overrun by yetis,...