On a snowy November day in 1997, in Flint, Michigan, police found the body of 45-year-old waitress Nancy Billiter. Her corpse had survived a botched attempt to burn it. An autopsy revealed that she'd been bound, beaten, sexually violated, and then injected with a lethal mixture of battery acid and heroin. Police suspected Nancy's friend, Carol Giles, and Giles's boyfriend, Tim Collier, who had often boasted of a murderous gangland past. As the law's...