A widow blames her husband's suicide upon a group of aristocrats who subsequently grabbed up all of his estate, leaving her destitute. She studies the arcane, pronounces her allegiance to the devil, and decides to create a Frankenstein monster in order to wreak vengeance. She funds her studies by performing seances under a new name until one of her intended victims hires her, recognizes her, and decides to finance her and provide her with facilities for her research into the arcane, in which he shares an interest. Most of this history is provided through narrative. The bulk of the film then deals with her eventually creating a monster (a tall, bald man who keeps one eye shut, is covered in white powder and has scars drawn on with mascara) while keeping her exact activities secret from her clueless benefactor. Except for a hillarious early 1970s fashion show sequence, and a little cheese here and there, this film is extremely dull and moves far more slowly than any of the old Hammer Frankenstein movies, while lacking their wit. It does have an evil dwarf (a guilty pleasure of mine), but he is completely wasted (he just hides in the basement until the villainess decides to kill him for no reason). As with most bad horror films, the police who investigate the various murders(when we finally get to them), as well as all those occupying the castle where this all takes place, fail to get a clue until the very end of the film.
Although I also consider Lady Frankenstein to be weaker than any of the Hammer Frankenstein films, it is a better female-lead Frankenstein-style-monster film than Devil's Kiss. In conclusion, this film is a renter, not a buyer. It may be worth noting the director never made a second horror film.