When their father is taken away one night for reasons nobody will explain, Roberta, Peter and Phyllis move with their mother to a small house in the country beside a railway line. The line becomes their world: they wave to the London train, make friends with Perks the porter and an old gentleman who travels on the 9.15, save a train from a landslide by waving red petticoats, rescue a boy hurt in a tunnel and shelter a Russian exile. Roberta slowly learns the truth about their father, and the ending on the station platform is one of the most moving in children's books.