when father goes away with two stranges one evening, the lives of roberta, peter and phyllis are shattered. they and mother have to move from their comfortable london home to go and live in a simple country cottage, where mother writes books to make ands meet. however they soon come to love the railway that runs near their cottage, and they make a habit of waving every day to the old gentelman who rides on it. they befriend the porter, perks and through him learn railway lore and much else. they have many adventures and when they save a train from disaster, they are helped by the old gentelman to solve the mystery of fathers disappearance and the family is happily reunited.