With several briefs in the works and his usual typist unavailable, Perry Mason sends for one from a temp agency. Everyone notices she's terribly afraid of something, and when later that day the offices of the South African Gem Importing and Exploration Company, located on the same floor as Mason's office, are rifled, the typist disappears.

And with the introduction of South African Diamonds into the case, it isn't long before murder follows, and Mason, assisted by his inimitable secretary Della Street and his private investigator Paul Drake, undertakes the intricate job of investigating the mystery.