There are at least two different works with this title. The first with an introduction by Ellery Queen (and published in England in 1949 by Faber and later by Penguin) contains ten stories; the second, edited and introduced by E. F. Bleiler (published in 1978) contains 14 stories. Only five stories are in both collections. This is the second title. Please do not combine with the other edition as they are not the same work.

There are at least three works with this title. The contents of the three works differ, so should remain separated. This work is the Bestseller Mystery title (No. 891) containing ten stories and an introduction by Ellery Queen. Please do not combine with other versions of this title.