The key image of this film occurs early on, as a hideous monster removes its face, only to reveal itself as Baron Frankenstein in a mask. Hammer's fifth installment in the series sees the transformation of doctor into monster complete. Peter Cushing's portrayal of the Baron here is all insanity and hatred, rather than the misunderstood (if unethical) genius of previous entries. Frankenstein transplants the brain of an insane doctor into Freddie Jones' body, creating a pathetic, misshapen beast, while using blackmail and rape to control the people around him. This was director Terence Fisher's favorite film, and his pacing and composition have rarely been better. Jones (the nasty showman in The Elephant Man) is great at communicating the disorientation and helpless agony of his condition, and while Cushing's character is more one-dimensional than usual, he does his normal excellent job as the Baron. Hammer's next installment was the silly Horror of Frankenstein before Fisher returned to end the series with Frankenstein and the Monster from Hell.
by Robert Firsching synopsis