Roberta ( also known as Bobbie), Peter and Phyllis live in a comfortable home in London with a wonderful mother and father as well as a maid. One day their father leaves home with two men. He is actually taken away to prison but the children do not know this at first. When he leaves and does not come back, they have to move to a poor cottage in the country (rural area) near a railway station. The children become familiar with the passing trains, the workers at the train station and signal-box, and life in a small town while their mother struggles to make ends meet by writing stories.
They learn to live with what little they have and they get used to being poor. They also learn not to steal coal from the railway station, even if they have so little to keep warm. They have various adventures – stopping a train when a landslide covers the tracks, finding an injured older boy in the train tunnel and getting help, while dealing with the mystery of their fathers disappearance. Sometimes they argue and have crises, but in time they make many new friends.
They also experience amusing adventures aplenty which happen near the railway and the canal. The children develop the habit of waving to the train as it goes past and sometimes the people in the coaches wave back. Their friendly gestures forge a special friendship with one person in particular, who goes by in the train. He then eventually gets to know them, and helps them out in various ways. Then, one day a train calls at the station and the children are pleasantly surprised to see their father. They are finally re-united.