Edinburgh, 1826: Corpses begin to turn up in Hangman's Wynd, one of the many dank alleyways that coil through the city's Old Town. Initially, the deaths are attributed to cholera morbus, an intestinal ailment rife among the residents of the Old Town's squalid tenements. But to David Arnesen, a professor at the city's medical school, it seems beyond chance that the victims are all prostitutes and that they die of the same symptoms in the same out-of-the-way location. He is certain the women are being murdered. But how? And why? And by whom? Using the tools of the new science of forensic medicine to pursue answers to these questions, he is led to a startling discovery...and nearly becomes another of the killer's victims.