In 1634, a small French convent of nuns is struck by mass hysteria when visions of ghostly men are seen on the property. But chaos enues when one nun suggests that the one causing the drama is none other than a handsome local priest who has made a pact with the devil. Hysteria leads to public exorcisms in a notorious witch hunt and trial that would shake the world of Catholic France and become known as the most famous case of its kind. This is the possession of Loudun.

Sources:
The Devils of Loudun- Urbain Grandier and the Possessed Nuns of Loudun by Bad Ideas
"Loudun Possessions" Occult World
"Looking Back: The possessions at Loudun" by Craig E Stephenson