The story concerns a family who move from London to 'The Three Chimneys', a house near a railway, after the father, who works at the Foreign Office, is imprisoned after being falsely accused of spying. The children, Bobbie, Peter and Phyllis, befriend an old gentleman who regularly takes the 9:15am train near their home; he is eventually able to help prove their father's innocence and the family is reunited. Before Father is freed, the family takes care of a Russian exile, Mr. Szczepansky, who came to England looking for his family and Jim, the grandson of the Old Gentleman, who suffers a broken leg in a tunnel.