The Clue of the Black Keys  The Clue of the Black Keys is the twenty-eighth volume in the Nancy Drew mystery series. It was first published in 1951 under the pseudonym Carolyn Keene. The actual authors were ghostwriters Wilhelmina Rankin and Harriet Stratemeyer Adams. Terry Scott went to River Heights to ask the help of Carson Drew to help him to find Dr. Joshua Pitt. Mr. Drew thought that the case was more of a mystery, so he referred him to Nancy Drew, his daughter who loves detective work. Terry Scott and Dr. Joshua Pitt, together with their teammates, Dr. Anderson and Dr. Graham, found the clue to the treasure during their expedition in Mexico, a cipher carved in a stone tablet and three black keys. Before the professors had time to translate the cipher, the tablet disappeared together with Dr. Pitt, leaving only the bottom half of one of the keys. Terry suspected the Tinos because they vanished when the cipher stone and Dr. Pitt disappeared. Someone tried to steal the half-key. Sergeant Malloy helped them identify the thief, Juarez Tino, but not until after he fled for Florida. Terry gave the half-key to Nancy and that night a burglar broke into the Drews' house. A thief stole Terry's things and documents from the hotel room. He thankfully did not steal the key. Nancy asked her father's advice, and he suggests finding the other expedition members. Nancy and George meet with Dr. Graham, and he says the four expedition members trust one another. Ned Nickerson asks Nancy to drive his fraternity brother in Emerson College, Prof. Terence Scott, to his lecture. Bess and George trail Mr. Porterly, and overhear his telephone conversation planning harm to Nancy. Anderson tells Nancy that Mr. Juarez Tino telephoned to say that he'd reveal where the cipher and Doctor Pitt are for a price. After Terry Scott's lecture, Mrs. Lillian Wagnell asked him to decipher her sea captain grandfather's old diary. Nancy doubts Mrs. Wagnell's intent, and Mrs. Prescott mentions that Mrs. Wagnell doesn't have a sea captain grandfather. Wagnell doesn't want Terry to borrow the diary so Nancy suggests he take the important pages. Carson Drew received a letter from Caswell P. Breed in Baltimore, a relative of Dr. Pitt. The Drews went to Baltimore but Mr. Breed sent no letter. They guess that someone has lured them out of River Heights for some nefarious purpose.