Basically another retelling of Dr. Jekyll and Mr. Hyde. Lee plays a Nineteenth Century psychologist who discovers a new formula that erases human inhibitions. At first he intends to use his patients as guinea pigs, but after discussing things with his pal and fellow doctor Peter Cushing, he decides to use the drug on himself. What results is a vile, ugly creature with a penchant for extreme violence, which he seems to enjoy immensely. Eventually, Lee loses control of his experiment and is no longer able to return to normal. Cushing gives a fine performance, but this is Lee's film all the way. Nice to see Raven in a solid supporting role. Good fun! Great color, 35mm.