Inferno ratings (Movie, 1980)

Riddled with secret but horrid suspicion, the young American poet, Rose Elliot, writes to her brother and musicology student in Rome, Mark, about the startling findings in the dark and dank basement of her New York Art Deco apartment building. Pivoting around the cryptic knowledge hidden in the leather-bound book entitled "The Three Mothers", Rose is convinced that her aristocratic but damned abode is, in fact, an ancient coven for Mater Tenebrarum, the malevolent Mother of Darkness. Little by little, as the siblings delve deeper and deeper into the occult, a mysterious disappearance and an endless string of gruesome killings will bring Mark closer and closer to a surreal nightmare. Where do the long and shadowy corridors of Rose's building lead?