Another exciting mystery begins for the  young detective when her friends Bess and George ask her to investigate a rumor that their wealthy great-granduncle, Asa Sidney, is virtually a prisoner in his own mansion. But solving the mystery and befriending Carol Wipple, the sixteen-year-old foster daughter of the caretakers of the old mansion, nearly costs Nancy the friendship of Bess and George. It takes all of Nancy's sleuthing ability as well as diplomacy to save it.

Nancy braves one danger after another to bring to justice the swindlers who are stealing Asa Sidney’s fortune. With only the sign of the twisted candles to guide her, Nancy uncovers hidden treasure and an amazing letter that ends a family feud and brings unexpected happiness to Carol.