Although not officially part of the 15 books in the Secret Seven series, this story actually marks the first adventure featuring the group. Peter and Janet first appeared in the 1947 book At Seaside Cottage, and the formation of the Secret Seven was later revealed in Secret of the Old Mill in 1948.
This is a short book, only 47 pages long, so it feels more like a novella than a full-length novel. That may be why it's not included in the main series. The story begins with Peter reading The Secret Society, which inspires him to create his own “secret band of boys and girls,” complete with a password and a meeting place. Instead of using the shed at the bottom of the garden, as seen in later books, the children choose the dilapidated Old Mill as their meeting spot. However, they quickly discover that they’re not alone there. Is it haunted, or are the “spirits” just people with their own secrets?
