Though the children don't know it at the time, their father, who works for the foreign office, has been arrested on charges of espionage. Although he is innocent, he is in jail. The servants know what is going on, as does the mother does, but all the children know is that their father is away somewhere.
For financial reasons, the mother relocates the family to a "ducky dear little white" house in a small village. Their mother explains to the children that "we've got to play at being Poor for a bit."
The three children—Roberta (called Bobbie), Peter, and Phyllis—are not happy when they first arrive at the Three Chimneys, their new home. It seems a barren place, and they hear what are either rats or mice in the walls. Because their mother is busy earning money as a writer, and they don't have funds for entertainment, the children are left to amuse themselves visiting the nearby railway station, standing on the platform and watching the trains go by. They eventually grow to love the station.
The children have to cope with not having as much coal for the fire as they would like and having either butter or jam with their bread, but not both. However, they mature and grow self-sufficient from having to look out after themselves.
The girls, especially Bobbie, the oldest, but also Phyllis, show that they are just as capable as boys of coping with adversity, while their mother shows she can earn a living.