It was the 1950s in postwar America, and paperback books were the hot new product in the publishing industry. Of course, to stand out from the crowd and sell, one needed a gimmick. Into this newly exuberant market came a publishing house named Ace Books, with the seductive promise of two books for the price of one. It also had the eye-catching premise of two separate covers, joined at the spine like Siamese twins. Finished with one book? Flip the paperback over and begin again with a new novel, complete with its own package. It was something completely different -- and it sold! 'Double Trouble' tours the short yet popular era of the Ace Mystery Doubles, and includes both author-title and title indexes for easy reference.