Enid Blyton The Secret Seven 12 Story Collection in 4 Books 3 in 1

Book 1: The Secret Seven (first published in 1949)
Book 2: Secret Seven Adventure (first published in 1950)
Book 3: Well Done, Secret Seven (first published in 1951)
Book 4: Secret Seven on the Trail (first published in 1952)
Book 5: Go Ahead, Secret Seven (first published in 1953)
Book 6: Good Work, Secret Seven (first published in 1954)
Book 7: Secret Seven Win Through (first published in 1955)
Book 8: Three Cheers, Secret Seven (first published in 1956)
Book 9: Secret Seven Mystery (first published in 1957)
Book 10: Puzzle For The Secret Seven (first published in 1958)
Book 11: Secret Seven Fireworks (first published in 1959)
Book 12: Good Old Secret Seven (first published in 1960)