The third and most original take on the old story that Hammer Films ever produced. In fact this is probably the most original take anyone has ever produced. Although remaining in their Gothic, Victorian roots, even in the 1970's, Hammer were still producing works of great imagination and originality. The script was written by Brian Clemens, largely a writer and producer for television, he enjoyed great success with The Avengers TV series in the 60's and The Avengers revival, The New Avengers and another popular espionage show, The Professionals in the late 70's. He would also go on to write and direct another Hammer cult classic, Captain Kronos, Vampire Hunter. The only film he would actually direct in his long career and in 1974, he would write the script for Ray Harryhausen's The Golden Voyage of Sinbad. This guy had real pedigree.
Clemens' approach was very different to every other Jekyll and Hyde story. Whereas all versions followed Jekyll in his quest to separate personalities, the good from the evil Ralph Bates' Dr Jekyll is more concerned with prolonging life. To be more specific his life in order to grant himself the time to complete his research. Jekyll's obsession compels him to acts of murder even before his alter ego shows up to carry on his work. Using female hormones, because he reasons that women live longer than men and have more resilience, he first removes these hormones from cadavers and later living subjects in this case prostitutes. Here, the film proves it's consistent inventiveness, not only from the plot perspective but also in its use of legendary real life grave robbers, Burk and Hare, although in reality, those two gentlemen actually operated in and around Edinburgh in Scotland and not London and also the incorporation of Jack the Ripper, tying in the murders committed by Jekyll and later Sister Hyde to the Ripper's real life killing spree in the Whitechapel area of London in 1888.
Even though Jekyll discovers quite by accident that he has prolonged the life of a common house fly, his colleague notes that the fly has also spontaneously changed sex. Intrigued, Jekyll produces a serum and tests it on himself. The transformation is handled with great subtlety, no dissolves or witnessing the transformation happening in full view of the audience. The effect is actually sold almost entirely on the striking resemblance, actress Martine Beswick shares with Ralph Bates. It is totally believable as they could actually be brother and sister. Beswick's performance is decadent, self-indulgence, seeming far more comfortable in her female body than inhabiting Jekyll's awkwardness.
The film is notable for its dark sense of humour and its ambiguity in addressing Jekyll's sexuality. Of the two siblings sharing the apartment above his, Jekyll seems far more drawn to the brother than the sister regardless of whether or not he is in the body of Jekyll or Hyde. In other versions Jekyll is clearly defined as good, Hyde as evil. Here both Jekyll and Hyde place themselves above the mediocrity of every day morality. The end justifies the means. It is these layers to the story that possibly make this the most interesting version of Jekyll and Hyde ever put on screen. Way ahead of its time and clever with it.