When Father goes away with two strangers one evening the lives of Roberta Peter & Phyllis are shattered. They & their mother have to move from their comfortable London home to go & live in a simple country cottage where Mother writes books to make ends meet. However they soon come to love the railway that runs near their cottage & they make a habit of waving to the Old Gentleman who rides on it. They befriend the porter Perks & through him learn railway lore & much else. They have many adventures & when they save a train from disaster they are helped by the Old Gentleman to solve the mystery of their father's disappearance.