Enid Blyton 
Secret Seven on the Trail [EPUB ebook] 
Secret Seven #4

Jack’s annoying sister, Susie, forms her own Secret Society – The Famous Five. They have a meeting in the summer house, and make up a tale about a gang meeting at Tigger’s Barn, for the benefit of Jack, who is hiding and listening by the laurel bush. Peter doesn’t believe Jack’s tale, and so to prove him wrong, Jack and George go along to Tigger’s barn, thinking they are following Susie and her friend. But it is soon clear to both boys that they are in the middle of an adventure, when two men creep into the tumble-down house and signal to Zeb to join them knowing the coast is clear! But then they discover George and think he has a message for them from Cheeky Charlie!