The story follows the lives of three siblings, Roberta, Peter, and Phyllis, whose father has been falsely imprisoned. They move from London to a rural village with their mother and become friends with the local railway porter, Perks. They also spend time waving to the passengers on passing trains, and eventually, their efforts lead to the discovery of the truth behind their father's imprisonment. The novel has been adapted into several films, television series, and stage productions.