Martin and Andy along with their cousins Kes and Mike are at the start of a 6 week holiday in Wales. As the rain pours down they are less than excited about the prospect. Everything changes when they are whisked away to another world by the mysterious dog Blenheim, who guards the secret doorway between the worlds. They are to help him defeat treacherous villain, the Bog, who threatens Blenheim's world and then plans to break through the very doorway into their world. He leads them on a roller coaster adventure where they meet new friends including a very smelly merchant and his old pack horse, a Lara Croft lookalike and a talking head. They also encounter terrifying villains, a dragon like monster and a terrifying wild tiger as they help Blenheim to face the Bog and to find his world's greatest hero who has not been seen for many years.