(From the publisher):
Terry Scott, a young archeology professor seeks Nancy's help in unearthing a secret of antiquity which can only be unlocked by three black keys. While on an archaeological expedition in Mexico, Terry and Dr. Joshua Pitt found a clue to the buried treasure on a cipher. Soon after, Dr. Pitt and the cipher disappeared. Terry suspects the Tinos, a couple posing as scientists who vanished at the same time.
Original title: The Clue of the Black Keys
Genre: Fiction→ Children & Young Adult→ Mystery