The murder case falls into the hands of Inspector Richard Queen of the Homicide Squad and his mystery-writing son Ellery.

A set of onyx bookends in the private apartments on the top of the store reveal not only bloodstains but grains of fingerprint powder and an unusual assortment of books.

At the finale of the novel, Ellery Queen performs an extended piece of deduction by creating a list of conditions that the murderer must meet (involving, among other things, the possession of keys).

The character of Ellery Queen and the more-or-less locked room mystery format were probably suggested by the novels featuring detective Philo Vance by S.S. Van Dine, which were very popular at the time.

"I state without reservation that the reader is at this stage in the recounting of The French Powder Mystery fully cognizant of all the facts pertinent to the discovery of the criminal; and that a sufficiently diligent study of what has gone before should educe a clear understanding of what is to come."