The Devils of Loudun - Aldous Huxley

Penguin classic mass market 1970's 

It is a historical narrative of supposed demonic possession, religious fanaticism, sexual repression, and mass hysteria that occurred in 17th-century France surrounding unexplained events that took place in the small town of Loudun. It centers on Roman Catholic priest Urbain Grandier and an entire convent of Ursuline nuns, who allegedly became possessed by demons after Grandier made a pact with Satan. The events led to several public exorcisms as well as executions by burning.  The book, though lesser known than Huxley's other books, is considered one of his best works. Wiki