In 1927, eight-year-old Clara Harrington's magical childhood shatters when her mother, renowned author Bronwyn Newcastle Fordham, disappears off the coast of South Carolina. Bronwyn stunned the world with a book written in an invented language that became a national sensation when she was just twelve years old. Her departure leaves behind not only a devoted husband and heartbroken daughter, but also the hope of ever translating the sequel to her landmark work. By 1952, Clara is an illustrator raising her own daughter, Wynnie. When a stranger named Charlie Jameson contacts her from London claiming to have discovered a handwritten dictionary of her mother's lost language, Clara is skeptical. Compelled by the tragedy of her mother's vanishing, she crosses the Atlantic with Wynnie only to arrive during one of London's most deadly natural disasters -- the Great Smog. With asthmatic Wynnie in peril, they escape the city with Charlie and find refuge in the Jameson's family retreat nestled in the Lake District. It is there that Clara must find the courage to uncover the truth about her mother and the story she left behind.