I, Monster is a version of Robert Louis Stevenson's 'The Strange Case of Dr. Jekyll and Mr. Hyde' made by Amicus Studios, who were most famous as the horror anthology specialists of British horror. This is one of their standalone entries. Their bigger contemporaries Hammer Studios had in fact released their own version of the famous novella also in 1971, namely Dr. Jekyll and Sister Hyde. Even just going by the title of the latter it's obvious that Hammer were going off on a clearly different angle with their adaption. As far as Amicus version is concerned, it's seemingly one of the most faithful versions of the story ever made. Interestingly, despite the source novella being in the public domain, both the title and character names are quite different. But when you see it, it's pretty obviously the same story. It's not clear why they chose to do this, although it may have been to give the film a slightly fresher feel.
The story has a doctor called Marlowe developing a drug that releases his patient's inhibitions, for example, turning a sexually repressed woman into a nymphomaniac. To further test it he starts taking it himself. It turns him into Mr. Blake an evil man who grows increasingly more physically repulsive the more times he takes a dose. Marlowe is ordinarily a very inhibited and cold man, whereas Blake is libidinous and carefree. Needless to say he is also murderous too and soon there is a manhunt on to discover who is responsible for these crimes.
Amicus made a fairly commendably earnest adaption here it has to be said. The production benefits from some authentic Victorian England locations and like other costume horrors from Britain from the period, its low budget is hidden quite well by the sets and costuming. It also has the two British stalwarts of the genre at its disposal in Christopher Lee and Peter Cushing. Lee has a fair bit to sink his teeth into in this dual role as Marlowe/Blake and he puts in a very good performance. Cushing is solid as he ever is but his role is very run-of-the-mill for him really and he doesn't get to do much beyond what we've seen him do umpteen times. Despite being quite faithful to the original source there are some amendments that have been added to make it slightly more modern such as Freudian theory underpinning things or the fact that Marlowe uses an intravenous drug as opposed to drinking a potion. On the whole though, like lots of these Amicus/Hammer period horrors, this one is solid more than great. There consequently isn't anything too surprising but if you are a fan of the sub-genre then this is certainly a good enough example.
