The story involves Nancy Drew helping her friend Emily Crandall find out who stole her heirloom jewels. Emily's aunt and guardian, Hazel Willoughby, unwisely removes them from a safe deposit box and carries them with her while lunching at Lilac Inn, only to have her handbag stolen while the diners are distracted. In the meantime, Nancy must hire a temporary maid in the absence of Mrs. Gruen, her housekeeper. Nancy uncovers the thief, Mary Mason, one of the applicants for the position of maid. She then tracks Mary Mason to a gang, which includes Mary's brother, Bud. Nancy is bound and gagged and left aboard the gang's sinking cabin cruiser to die, but is rescued by the river patrol. In the end, Nancy captures the jewel thief, exonerates the guardian, and returns her orphaned friend's fortun