The Secret Seven series of 15 books, by prolific author Enid Blyton, follows the adventures of a strictly secret society made up of 7 children, who like to solve mysteries that they happen upon, or actively go looking for!
Although many may think, like I did before doing this research, that The Secret Seven - the first title in this series - is the first time we are introduced to the seven, this is not the case. In 1947, At Seaside Cottage a small volume was published by Brockhampton Press and featured the main characters of Peter and Janet, with their golden spaniel, Scamper. A year later in 1948, Secret of the Old Mill was published, in which Peter and Janet, after reading a book called The Secret Society, decide to create a secret society of their own, using the old mill on a hill near their home as a meeting place. They invite five of their friends to join them, and so The Secret Seven are born.