Good Old Secret Seven

The Secret Seven are Peter and his sister Janet, Jack, Colin, George, Pam and Barbara. They meet every holiday in the shed at the bottom of Peter and Janet's garden - and solve mysteries, and eat lots of delicious food. But no one can enter the shed without whispering the secret password! There are 15 Secret Seven novels, and a collection of short stories.
There are strange happenings at Torling Castle. Someone is hiding out in the ruined tower, making the resident jackdaws very unsettled.
Who is it - and what do they want The Secret Seven are on to it ...
Each book features rarely seen bonus Blyton: extra stories, a quiz, additional artwork and insights into Blyton's life and writing process.