Mystery of the Skull is the sixteenth book in Enid Blyton's Secret Seven series. The Secret Seven Society—Peter, Janet, Jack, Barbara, Pam, Colin, and George—are a group of child detectives who hold secret meetings. The plot centers on the discovery of a mysterious skull, which leads the Seven on a new, perplexing investigation to uncover its origin and the secret surrounding it. The story tests the children's teamwork and detective skills.