Secret Seven Mystery: 9 (The Secret Seven Series) is a children's adventure story book. Part of the Secret Seven series, the book narrates one of the many adventures of the Secret Seven, a detective community made up of a group of children. Peter, Janet, Barbara, Jack, Pam, George and Colin make up the secret seven society and with peter as the leader of this group. The book narrates a particular case they encounter when a young girl named Elizabeth Sonning, accused of stealing money from her mistress, disappears. The gang comes together to study the situation. They split up looking for clues Peter and Jack head over to Elizabeth's grandmother's house, Barbara and Pam take to searching the woods, Colin decides to check out the barns and shelters in the neighbourhood, while George and Janet investigate the stables nearby enquiring about Elizabeth being spotted there.