In 1960s Oxford, Professor Henry Lytten is attempting to write a fantasy novel that forgoes the magic of his predecessors, J.R.R. Tolkien and C.S. Lewis. He finds an unlikely confidante in his quick-witted, inquisitive young neighbor Rosie. One day, while chasing Lytten's cat, Rosie encounters a doorway in his cellar. She steps through and finds herself in an idyllic, pastoral land where Storytellers are revered above all others. There she meets a young man who is about to embark on a quest of his own--and may be the one chance Rosie has of returning home. These breathtaking adventures ultimately intertwine with the story of an eccentric psycho-mathematician whose breakthrough discovery will affect all of these different lives and worlds.