'What if my great-grandmother is a witch!' thought Tolly, as he journeyed by train across the waterlogged countryside towards his great-grandmother's house. She wasn't a witch, but both she and her old house, Green Knowe, were full of a very special kind of magic. And Green Knowe turned out not to be the lonely place Tolly had imagined it to be. There were other children living in the house - children who had been happy there centuries before....