The story begins with a model in the ground-floor store window of French's Department Store in New York City who is demonstrating the features of a suite of ultra-modern furniture. When she pushes a button to reveal the folding bed, the bludgeoned corpse of the wife of the owner of the store tumbles to the floor.
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. Also, an ashtray full of half-smoked cigarettes is an important clue. The suspects include the wealthy victim's family and friends, some employees of the store, and possible members of a drug ring.
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). He clears all suspects except one, whose identity is revealed in the last line of the novel.