Nancy Drew Mystery Stories #11: The Clue of the Broken Locket book by Carolyn Keene

Another vacation turns into a riddle for Nancy to solve while she visits a lakeside holiday area. Cecily Curtis seeks the girl sleuth’s help in solving two mysteries. One concerns her fiancé, a popular singer who believes his record company is cheating him. The other involves a hidden family treasure; the only clue is half of a gold locket. Strange circumstances provide Nancy with many opportunities to test her sleuthing skills and discover the astounding secrets of Pudding Stone Lodge.