At the dawn of the 20th century, three Waterbury children – Bobbie, Phyllis, and Peter – find themselves involved in unexpected dramas along the railway by their new home in Yorkshire. Following their father's wrongful arrest on suspicion of betrayal, the family moves to a humble house near Oakworth railway station, where they befriend Albert Perks, the station porter, and an elderly gentleman who regularly takes the 9:15 train. With their mother working as a writer and homeschooling the children, Bobbie writes letters to the gentleman for help, leading to the reunion of the family with her father after he is exonerated and released from prison.