Jim Raymond, Junior Captain of the Monks' Court School, and the "Company of Four" who share his study, spend the summer term unravelling the mystery surrounding Koromoff, a new boy reputed to be the son of a South American diplomat. Many are the adventures, both thrilling and comic, that follow, and the four friends are hindered rather than helped by the fat and greedy Podger Pepys who can never stay our of trouble for long.