Lovely young Carla Ponce, who lives in Peru, invites Nancy and her friends Bess and George to visit her and solve her monkey mystery, which promises to lead to a fabulous treasure. A clue is carved on an intriguing wooden plaque that is so old, most of the crossword cipher is obliterated. When a notorious gang headed by El Gato (the Cat) steals the priceless relic, Nancy s hopes of solving the mystery are almost shattered. But the daring young detective s ability to think fast and act quickly results in the recovery of the plaque.
Nancy s determined efforts to decode the crossword decipher take her to the magnificent, awe-inspiring Incan ruins at Cuzco and Machu Pichu. Through clever deductions, perseverance, and dangerous adventures, Nancy and her friends help to capture a ring of vicious smugglers and go on to make an astounding archaeological discovery."