At the end of World War II, Baron von Rhoneberg (Jean Servais) sacrificed his daughter instead of allowing her to live her life under the family curse. That curse? Each first born daughter must become a succubus. Somehow, even though he was a general during the war, he isn’t charged with war crimes — or you know, murder — and his castle is famous enough that it brings a reporter who starts taking photos. He tells her not to, as he lives a hidden life, but she does anyway and is hit with a bolt of lightning out of nowhere that leaves the mark of the devil on her. And oh yeah, she’s dead now.

Welcome to The Devil’s Nightmare, which is also called La plus longue nuit du diable (The Devil’s Longest Night) and La terrificante notte del demonio (The Terrifying Night of the Demon). It also has the titles The Devil Walks at Midnight, Succubus, Vampire Playgirls, Satan’s Playthings and Castle of Death. It played U.S. triple bills with In the Devil’s Garden and The Devil’s Wedding Night.

A group of seven tourists — Matt, Nancy, Howard, Corinne, Regine, Mr. Mason and Alvin — are stranded when a flood takes out a bridge. Satan himself — well, they don’t know it yet — directs them to the Baron’s castle, where his servant Hans (Maurice De Groote) gets them rooms for the evening and informs his master that he has guests. The Baron is in the middle of doing some alchemy but still has time for dinner, during which he explains his family curse. When asked if he has a daughter, he answers to the contrary.

Meanwhile, Lisa Muller (Erika Blanc) is another guest and she goes about killing each of the other guests following the rules of the seven deadly sins. Only Alvin, a seminary student, survives her murderous ways. He asks Satan if he can save the souls of everyone else by giving up his own. The devil agrees and everyone is back alive.

The next morning, the Baron reveals to Alvin that he killed his daughter when she was a baby, but the joke is on him. The housekeeper Martha reveals that her daughter is Lisa and that her father is the Baron’s brother, making her the first-born woman of this generation of the von Rhoneberg family. Alvin refuses to believe that Lisa could be a demon and stays with her at the castle as the rest of the group drives off, soon run off the road by a hearse driven by Satan, dooming everyone all over again and getting Alvin’s soul too. He and Lisa smile at each other.

You can read my past review of this that was posted when Mondo Macabro released it and Jenn Upton’s article on the movie as well.