When they move their meeting place to a hidden cave, the Secret Seven stumble across evidence of a mailbag robbery.

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. The Secret Seven have a brand-new meeting place, but somebody else has been using it too! Whoever they are, they'll return at night - and the gang are determined to put a stop to it. They'll catch the cheeky intruder, whatever it takes ... Each book features rarely seen bonus Blyton: extra stories, a quiz, additional artwork and insights into Blyton's life and writing process.