The Gabriel Hounds

This Mary Stewart book was printed in 1967. It's a boys own type of story set in the Middle East long before ISIS ever came along.  Castles being scaled in the dark to find secret passage ways into the old Harem court.  I remember reading her three book series on Merlin. These must have been the next project as they started appearing in the 1970s. This book has many references to Lady Hester Stanhope an English aristocrat who became Queen of the Desert. The price on the back is 95c.