We know very well that traveling in the 1970s was a dangerous thing, but in the end "weaned" young people who opened up new experiences. We have seen it in many films. Not to mention the ever-amazing, lesbian vampires.
Even Joseph W. Sarno one day follows this wake, which represents for him, who loved talking about the middle-class, a great novelty.

The occasion comes with the German producer Chris Nebe, a great fan of the filmmaker and especially grim of working with him. Nebe also has a relative who has a castle, which could be used as a location. In fact, it is used as a location for a story written by Sarno himself who speaks of vampires. Actually, vampires that are in Germany.
"Der Fluch der schwarzen Schwestern" also known as "The Devil's Plaything" is an erotic horror that reminds by theme and atmosphere the Jean Rollin and Jess Franco's works (see the scenes of vampires dancing in topless on a rhythm of drums). They, moreover, were better suited to the context and certainly better to handle the "meat" of the situation.
In short, here we see the slowness of the films of Sarno, in the service of a not original story. However, we must admit that the American director is never trivial and use as its best, with its elegance, the (few) elements available.
The star here is Marie Forså, a Swedish actress, who then becomes an interpreter of several erotic films and who with Sarno makes two more films.
Therefore, we find a group of girls who end up in a castle on the German mountains. They also find a couple with car problems. The castle, however, is infested by the presence of vampire Baroness Varga, who rises and begins to bother the common mortals present there. Another seductive bite of the seventies.