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Twelve-year-old Linus, his mother and sister Linnea go to Trakeborg for the summer, to a quaint wooden house that has been empty for many years after the mysterious disappearance of its strange owner. It would seem that the summer will be boring and uninteresting, but on the first night the boy hears strange noises in the walls, and soon things start to disappear. When Linus goes to explore the house, he finds a mysterious key under the broken floorboards. Who hid it and what does it unlock? You will learn about this from the pages of the fantasy story The Key to the Underworld by Swedish writers Albin and Karin Alvtegen.