In 1906, Belle Gunness started running personal ads in Midwestern papers. She described herself as an attractive widow with a lush Indiana farm property, interested in an equally affluent new husband. She included a tart postscript: "Triflers need not apply."

Suitors answered her call by the dozen—and disappeared at a similar rate. After Ms. Gunness herself vanished in 1908, the La Porte, Ind. police department eventually set the body count at more than 40. This figure included her children and stepchildren, pieces of whom...