After the death of an elderly Greek man who is an internationally famous art dealer and collector, his attorney discovers that his will is missing and notifies the district attorney. When Inspector Richard Queen of the New York Police Force's Homicide Squad and his amateur detective son Ellery are called in, Ellery narrows down the possible location of the will to a single location: the dead man's coffin. When it is exhumed, however, it contains no will but the surprising addition of a strangled ex-convict.
Ellery performs an extended piece of deduction in public early on in the novel that concerns a number of used teacups, and is proved wrong. Stung by this embarrassing error, he keeps his deductions to himself for the remainder of the case. Subsequent clues involve color-blindness, a shred of the burned will, two copies of a Leonardo da Vinci painting differing only in skin tone, a thousand-dollar bill, a dead art dealer whose office door was either open or closed and, most importantly, an infinitesimal typing error.
Ellery and his father lay a trap, unmasking the murderer— whose guilt will probably have been entirely unsuspected by most readers.