The Thirteenth Pearl is the fifty-sixth volume in the Nancy Drew Mystery Stories series. It was first published in 1979 under the pseudonym Carolyn Keene. The actual author was ghostwriter Harriet Stratemeyer Adams. Although other volumes follow this one, "The Thirteenth Pearl" is the end of the original 56-book series published by Grosset & Dunlap.
Nancy's asked to locate a missing pearl that is unusual, but very valuable. She soon learns that dangerous people are responsible for the theft. They begin harassing her at home and it intensifies when Nancy and her father go to Japan. They finally kidnap her and her boyfriend, Ned when they return to River Heights. Through her clever sleuthing, Nancy is able to penetrate the rites of a pearl-worshiping cult, but some are far from devotion, and she uncovers underhanded dealings of certain employees of World Wide Gems, Inc., an international jewelry company headquartered in Tokyo, Japan.