Mary MacDougall's first case of 1902 seems simple enough. Just before the 19-year-old heiress leaves for a summer holiday on Mackinac Island with her Aunt Christena, she's hired to stop in a little town along the way and make inquiries. Did Agnes Olcott really die there of cholera? Or were there darker doings in Dillmont? Mary's mentor, Detective Sauer, thinks it's merely a case of bad luck for the dead woman. But Mrs. Olcott's daughter suspects her detested stepfather played a hand in her mother's untimely death. With the reluctant help of her aunt and her dear friend Edmond Roy, the young detective struggles to reveal the true fate of Agnes Olcott. As she digs ever deeper, the enemy Mary provokes could spell disaster for her and the people she loves. But in the end, it's the only way to banish a daughter's doubt.