In Cold War England, Professor Henry Lytten, having renounced a career in espionage, is writing a fantasy novel that dares to imagine a world less fraught than his own.
He finds an unlikely confidante in Rosie, an inquisitive young neighbor who, while chasing after Lytten's cat one day, stumbles through a doorway in his cellar and into a stunning and unfamiliar bucolic landscape—remarkably like the fantasy world Lytten is writing about. There she meets a young boy named Jay who is about to embark on a journey that will …