The Secret of the Caves - 1929
The Great Airport Mystery - 1930
The Mark on the Door - 1934
A Figure in Hiding - 1937
The Secret Warning - 1938
The Flickering Torch Mystery - 1943
The Tower Treasure - 1959
The Secret of the Old Mill - 1962
The six (6) older books are in Good - VG condition
The newer books are in EX condition