Belle Gunness was one of the most gruesome mass killers in American history. Her handiwork has been compared to that of the notorious French murderer, known as Bluebeard. She systematically murdered her husband and anywhere from 14 to 30 suitors; she may also have burned her own children alive. Yet to her neighbors in LaPorte, Indiana, Gunness was a middle-aged widow, the owner of a struggling hog farm, who advertised in the nineteenth-century version of the personal ads for a husband. Little is known of her early life, other than she was born in Selbu, Norway, and emigrated to the United States in 1881.

Gunness regularly ran the same ad, seeking a wealthy suitor and adding, "No triflers need apply." This request for a rich man was actually a common practice among poor women; while not a romantic embellishment it was a practical request, since no woman wanted to marry a...