The Mansion of Madness
(1973)

A rather faithful version of Edgar Allan Poe's "The System of Doctor Tarr and Professor Fether."

Gaston LeBlanc is a journalist traveling through France. He wants to write about the mental hospital run by Dr Maillard. When he arrives, he is surprised by how the hospital is run.  Maillard believes the insane should be given free rein to live out their delusions.  The patients run wild, with no order.  Gaston does not know it, but his driver is beaten to death by the patients.  He is also troubled when patients try to injure him, and Dr Maillard just laughs about it.  Gaston is horrified to discover a torture chamber in the basement.  Gaston sees a beautiful young lady, Eugenie, being torutured.  Gaston confronts Maillard, calling him a fraud and an imposter.  Maillard has the orderlies imprison Gaston in his dungeon.

Gaston escapes and takes Eugenie with him.  Eugenie tells Gaston that she is the daughter of the real Dr Maillard.  The man running the asylum is Raoul Fragonard, a criminally insane patient.  Fragonard turned against Maillard and has taken over the asylum.  The former doctors, nurses and employees are the people being tortured by the inmates.  Fragonard/Maillard enlists all his insane minions into a hunting party.   They capture Gaston and Eugenie and lock them in the dungeon. Fragonard celebrates a wild carnival dinner with his followers.

During the dinner, the locked up employees escape.  They invade the dining hall and battle the inmates for control of the asylum.  Fragonard proposes a one on one, man to man fight between him and Gaston for authority.  However, as they fight, one of the female lunatics grabs a gun and shoots Fragonard, ending the rule of the lunatics.

Thanks Joseph C!