What is The Monster of Florence about?

Between 1974 and 1985, a serial killer known as the Monster of Florence murdered sixteen people — couples parked in cars in the hills outside the city — and was never conclusively identified. Douglas Preston, an American thriller writer who moved to Florence with his family in 2000, became fascinated by the case and began investigating it with Mario Spezi, the Italian journalist who had covered the murders from the beginning. The Monster of Florence is their joint account — part true crime, part memoir of an investigation that eventually turned on its authors.

The Italian prosecution of the Monster case became increasingly bizarre over the decades. After several likely suspects died in prison or were acquitted, prosecutors developed a theory that the murders were committed for a Satanic cult of wealthy Florentines who used the victims' body parts in rituals. The theory was supported by almost no evidence. Preston and Spezi's investigation challenged it, and the consequences were severe: Spezi was arrested and charged with being the Monster himself, and Preston was interrogated by Italian police who suggested he was a suspect as well. Preston was told to leave the country. He did.

The book is at its strongest in two places. The historical reconstruction of the murders and the investigation's early years — conducted largely through Spezi's decades of reporting — is genuinely gripping, with real suspects, missed connections, and the kind of procedural detail that makes narrative nonfiction work. The second strength is the portrait of Giuliano Mignini, the Perugian prosecutor who ran the Satanic cult theory and later prosecuted Amanda Knox for a separate murder under similarly contested circumstances. Preston's account of Mignini reads as a profile of a specific kind of institutional overreach: a prosecutor who had invested so much in a theory that disconfirming evidence became threatening rather than instructive.

The Monster case was never conclusively solved. Several suspects remain plausible. The book ends with Preston and Spezi's best theory, which they present as probable but not proven. For readers accustomed to crime narratives that resolve, that ending can be frustrating. But it accurately represents where the case actually stands, and that honesty is more useful than a false closure.