The most interesting thing about I, Monster, a 1971 showcase for the great Christopher Lee released by Amicus productions, is also the most baffling. Not to spoil the surprise - the film has already spoiled itself, quite thoroughly - but the film is an uncredited adaptation of Robert Louis Stevenson's 1886 novella Strange Case of Dr Jekyll and Mr Hyde (sort of. Stevenson actually gets credit, without referencing the title of the book). It also changes the names of the title character(s), but only those names - they/he are/is now called Dr. Charles Marlowe and Mr. Edward Blake, played of course by Lee. I would say that it seems obvious why this has happened: writer-producer Milton Subotsky wanted to try and get back to the structure of the novella, which had never before to my knowledge before been attempted in all the dozens of film versions of the book stretching all the way back to 1908. For if you haven't read it, Stevenson's Strange Case is presented as a mystery, centered around the character of Utterson, a lawyer trying to figure out what has caused the strange changes in the character of his good friend Dr. Henry Jekyll. He finally learns, in the tenth of ten chapters (and by far the longest, taking up around a fifth of the book), that Jekyll has created a serum that allows him to... well, surely you know that part. Which is exactly why nobody has ever tried to film it that way; the shocking twist hasn't been shocking, or a twist, since before the movies even existed. And that's why all the most famous adaptations have instead been more directly based on the 1887 stage version of the story by Thomas Russell Sullivan.

Indeed, I, Monster is as far as I know the only real attempt to make a generally faithful screen adaptation of the novel that I have ever heard of, and it even gets pretty close to that target all things considered. So that's the most interesting thing. The most baffling thing is that, having gone to these lengths to do the impossible, the film immediately lets us know that Marlowe is developing his serum, and while the film does maintain the plot of the novella, devoting considerable time to Utterson's (Peter Cushing) investigations, and mostly relating the major events of the novel as he carries these investigations out, it cross-cuts them with the plot points that Chapter 10 retroactively reveals. That this ends up working is largely a testimony to Cushing, who has found a way to make all of this character material for Utterson rather than simply functioning as a dogged amateur sleuth, and not even with a lot of evident work to get to that point.

Still, with all thanks to Cushing for helping to limit the negative impact of this very odd decision, it's not his film. It's Lee's, and he makes an absolute feast of it; right offhand, the only one of his performances that I'm absolutely certain is better than this is his work as Lord Summerisle in The Wicker Man, two years later. Maybe it's a coincidence and maybe it's not that these are two of the only times I can think of where Lee wore something entirely out of character: a great big fucking smile. I don't mean to diminish the rest of his performance in I, Monster if I suggest that the single best thing Lee is up to, and the single best thing about the movie as a whole, is the smile he wears in his first two scenes as Blake. It is pulverisingly creepy - legitimately the most I've ever been freaked out watching Lee do anything. It's way too big, and it doesn't match his eyes: they're big and round, perfectly little bugged-out circles, with none of the creases your eyes are supposed to develop when you smile. And his mouth has a kind of rigid quality, like his lips have been turned outward and bent into place. Plus, he gets a lot of teeth in there. It's feral and uncanny, and it's a better effect than anything that happens when Blake inevitably starts to suffer the accumulative impact of the serum and gets all puffy-faced and baggy-eyed, and his nose begins spreading in all directions. I get why the film has to do start slathering Lee in make-up - two major plot points hinge on people who know Marlowe extremely failing to recognise him in Blake - but I still think it was a mistake; Lee's own natural face is all the special effects the movie needs to get to a place of bone-chilling terror. And it's superbly augmented by composer Carl Davis's unconventional, even atonal musical motif for Blake, a bouncy, almost carousel-like piece that feels like it's being played on the Devil's piccolos, and offers a freakish, jaunty mood that sonically reproduces the unnerving horror of Lee's grin.

This is just one facet of the performance, of course. The actor is also superb in exploring how Marlowe/Blake feels about all of this, and it's pretty impressive and unusual for a Jekyll & Hyde story. The short version is that Blake, the monstrous half of the doctor's personality, ends up being the more sensitive and miserable figure, repulsed by himself and angry at the revulsion he inspires in others, and sufficiently self-possessed to be horrified rather than emboldened when he breaks out. Marlowe, on the other hand, is fascinated by all of this, eager to keep running tests, and concerned more about keeping his secret than tormented by the damage he's causing (the film draws a pretty straight line between Marlowe's experiments and drug addiction, visually at least). This is all related to the film's new conception of what the relationship between the two identities is: Marlowe is besotted with the new theories coming out of Vienna and the pen of Dr. Sigmund Freud, and he has taken to treating patients using Freudian analysis. He's also convinced that he can use chemicals to, in effect "turn off" the id and the superego, and this is what his serum is meant to accomplish (the film is set in 1906, by which point I'm not sure that Freud's work had been translated into English, and I'm definitely certain the id-ego-superego model hadn't shown up in any of his writing yet). When we see him test it on patients, it seems more about letting their subconscious pipe up to have a say (the grown man turned into a terrified little boy can hardly be called a monster of uncontrolled id), but the unleashed id is a good enough way to think of what Blake represents - not, then, the evil elements of a good man. And, in fact, Marlowe never comes across as good man, not really; the first thing he does in the film just about, is to freak out and beat a cat to death after he injects it with the serum. He's perfectly ready to commit violence, that is to say, and Blake is still basically the same man, just less afraid of what people think of his behavior (this is part of why it's such a bummer that the filmmakers go all-in on make-up as the film progresses). There's no reason Blake can't have tenderness, self-loathing, and depression, given that, and the way Lee teases those things out makes this one of the most striking and unusual performances of the character type I've ever seen, right up there in its impact with Fredric March's definitive take on Jekyll & Hyde in the masterful 1931 film adaptation.

I am not certain that I, Monster could have done enough wrong to get on my bad side after hooking me up with that Christopher Lee performance. And to be fair, it does so some unmistakably bad things. The pacing is erratic as hell: the film is 75 minutes, which is a fair running time, if a touch on the short side, but within that, the movie is often either too fast or too slow: the middle scenes, when Marlowe descends deeper and deeper into Blake, buzz past at top speed, while the early scenes of Utterson laboriously noticing that Marlowe is a bit "off" seem to take forever to establish the blatantly obvious. And there's that whole matter of structuring itself as a mystery, when it has already given us the answer before it starts asking the questions.

Mostly, though, this is good, solid filmmaking, and often better. As Amicus's first (of two) horror films not to be set in the present day, I, Monster represents an opportunity to see what things might have looked like if the studio was willing to go head-to-head with Hammer Film, and the results are pretty impressive. Presumably these are all standing sets hanging around Shepperton studios (the film has no credited production designer or art director), but they've been used well, treated with a kind of cluttered, unadorned realism that never feels like it's trying to impress us with period authenticity, but simply to scatter Edwardian London at us as a collection of spaces that are lived in and get used. I would almost call it ugly, with cinematographer Moray Grant (a veteran of a great many Hammer productions, a cinematographer or camera operator) treating everything with flat lighting and slightly wide lenses to give everything just a hint of an exaggerted, unpleasant look. He and director Stephen Weeks also play around with a restless, twitchy camera, which keeps sweeping around rooms in little half-curvesΒ  and fluid tracking shots. It makes the whole movie seem unsettled and oddly curious, and it's great for making those sets feel more tangible and physical, by virtue of letting us pace around them a bit.

Taken all together, this is one of the strongest filmed versions of the Jekyll & Hyde story that I've seen. It lacks the formal perfection of the 1931 film or the unadulterated nastiness and wicked cleverness of Hammer's The Two Faces of Dr. Jekyll, from 1960 (which also featured Lee as a side character), but its attempt to pare the material back down to the matter of the book, and focus the attention entirely on Marlowe/Blake's descent into moral chaos, and Utterson's stubborn concern for his friend make it feel blessedly clean and straightforward. The Freudian angle, though dotty, comes as close as anything I think I've ever seen to answering the fundamentally unanswerable question of why Jekyll would choose to experiment with evilness juice, while also giving making this feel enough of its own thing to sell the re-titling and renaming. And Lee's horrible smile is, I state with the purest, most placid sincerity, the most disconcertingly eerie and upsetting thing I have ever seen in a British horror film. So a pretty great time all around, then, and coupled with the splendid anthology film The House That Dripped Blood, it provides a fantastic kick-off to Amicus's concentrated binge of horror movies in the first half of the 1970s, right at the moment that their competitor's horror productions were starting to go badly off the rails.