This film is impressive enough for me to spend much of this review grumbling that it falls short of greatness, which I think wasn't far from its grasp. It's a brave, imaginative adaptation of a classic horror fable. It also avoids the obvious traps of seeming cheap and gimmicky. I'd expected nothing but lowbrow schlock given that it's a version of Robert Louis Stevenson's Dr Jekyll and Mr Hyde in which the well-meaning doctor's alter ego is female, but in fact it's one of the better adaptations I've seen of what seems to be a deceptively tricky original. Believe it or not, it even spawned a sub-genre of cross-gender Jekyll & Hydes, which seem to be about as common as the film's other big idea of turning him into Jack the Ripper.

For starters, Martine Beswick not just acts but looks like Ralph Bates. Despite being beautiful and female, she's him to a tee. Ironically her impersonation is perhaps closer to his standard Hammer persona than his own performance on this occasion, since for once Bates is playing a genuinely nice chap. Perhaps not someone you'd want to take home to mother, not with his murders and his growing mental instability, but we get to see and understand the reasoning that led him there. He thinks he might find a cure for typhoid and cholera. If he'd really achieved that in late Victorian London, then who's to say that half a dozen murders wouldn't indeed have been worth it?

It's rare enough to see a convincing Jekyll-Hyde combination on screen, but it's downright spooky to see it achieved despite the gender divide. I'd also suggest that theoretically this should perhaps be a better story than Frankenstein. The mad scientist and his creation are one and the same. However I can't think of a great or even particularly memorable adaptation, perhaps because I don't think any actor's ever really managed to put their stamp on the role(s). I haven't seen the 1931 version, though. Ralph Bates probably had as good a chance as anyone ever has, since this version of Jekyll gets to fall into evil and madness all by himself. Ironically they give him so much good material that I was worried about what this would mean for Hyde. It doesn't seem to leave her much to do except be female. Admittedly this means nudity and so I'm all for it, but until Jekyll and Hyde ended up at open war with each other I wasn't sure where this was going to take the story.

In the end, it's a great role. Jekyll blames Hyde for the death of his friend, but given his mental state it's far from clear how much the two of them are dissociating. Are they really two people, or just one sick individual? Even when he's male, we see Hyde starting to affect Jekyll's habits in a manner that gives rise to amusing embarrassments with his neighbours. Corsets, mmmm. By the end he's writing down everything he's done in a journal for the sake of future scientists, which suggests either that he's lost contact with reality or that even he thinks he's doomed.

I'd also point out that Dr Jekyll is a brilliant fit with Jack the Ripper, fitting the medical dissection nature of the real murders. I don't even mind the film getting carried away by throwing in Burke & Hare, despite the fact that they were working in Edinburgh sixty years earlier. Surprisingly there's historical basis for their eventual fates here, despite the film's apparent 1066 And All That approach. There's even a possible nod to Sweeney Todd. I loved all that. There's something about the fog-and-prostitute London we see here that screams "Jack the Ripper" before you even learn that you're in Whitechapel. You couldn't mistake it for the Victoriana of Dickens or Sherlock Holmes. It's a wonderful world.

Everything was set up to be wonderful. Ralph Bates had a great role, perhaps the role of a lifetime... but alas he muffs it. Oh, he's thoroughly watchable. As the lead of a Hammer film, he's excellent. However he never makes it anything more than that. When the police hunt him down for the inevitable tragic climax, it's not particularly interesting and you're just waiting for the obvious to happen. "Couldn't they have put a victim in jeopardy?" you'll be wondering. The last five or ten minutes could be said to fizzle out, which is a crying shame since a bravura performance might have burned the story of Dr Henry Jekyll into your brain. Ironically there was another British Jekyll & Hyde film also in 1971, starring Christopher Lee and Peter Cushing! They did the obvious thing by giving Lee the dual role while making Cushing his staunch friend Utterson, but why oh why didn't they do it the other way around? Apparently Fredric March won an Oscar for the role in 1931 and I'm now almost desperate to see it.

I also think it was a mistake to dilute the morality of Stevenson's original. The men are appalling. Utterson is now a hypocrite and a swine, called Robertson. He gets a line about struggling with his conscience which I didn't believe for a moment. Jekyll's neighbour is a sexist git. My favourite performance comes from Philip Madoc (who should be in all movies ever made) as Ryker, a mortuary attendant who manages to be funny and charming despite being a depraved seller of corpses with possible necrophiliac tendencies. Stevenson's story was aware of the full horror of Jekyll's fall from grace, whereas this film wallows from the beginning in the sordid side of human nature. It's historically authentic and it makes for a richly atmospheric film, but I prefer the stark black and white of the original morality play.

The only exception to the general depravity is Susan Broderick's character, a truly beautiful neighbour of Jekyll's who's so sweet on him that she ends up seeming almost simple-minded. How many rebuffs can one woman shrug off? Broderick is adorable in a role that should have had me wanting to kick in my television and it's astonishing to me that she didn't stay longer in the industry. Quite apart from anything else, she really is stunning.

There's some pseudo-science daft enough to make Cushing's Frankenstein seem sane and rational. Apparently female hormones turn you into a superhuman immortal, but also change your gender. Someone should tell the Hormone Replacement Therapy industry. The exact nature of Jekyll's murderous dissections though is kept carefully vague, which is a good thing since any explanation they might have provided would have been bollocks. However Professor Robertson seems to have an oddly detailed knowledge of Jekyll's eccentric surgical requirements, despite one presumes not having been told anything about them.

Other goofs include a modern-looking bolt on a door. The soundtrack occasionally isn't quite synched correctly. Finally why does Jekyll accept Susan's invitation towards the end? Surely even he must have realised it was a mistake.

Small anecdote. Ralph Bates met his wife Virginia Wetherell when shooting a scene for this film in which she played a prostitute and he had to murder her.

This is an outstanding showcase for the Hammer formula, one of those rare movies in which their house style works so well with the subject matter that it doesn't feel dated. It's also more horrifying than I'd expected, at times to the point of being disturbing. Check out the combination of sex and violence in one imaginative gore shot. This isn't a bad film for lovers of the female form, with the beauty of Broderick, the nudity of Beswick and some memorably heaving decolletage. Mrs Hyde would have also made a fine vampire, waiting in that dress on London's fogbound streets. She's spooky. It's possible to criticise the film, but that's what you get when you adapt a classic. Like the 1940 Pride and Prejudice, it's not a work of genius. Instead it's merely a darned good movie.