A troubled teenager in a small American town struggles with his sociopathic inclinations, battling the murderous urges which lie within. His laid-back therapist and job at the family mortuary help keep his blood lust satisfied, poking at corpses generally being a decent substitution for creating them himself. But with a serial killer on the loose in town, murdering indiscriminately and stealing organs, John may well be pushed over the edge – especially as his already tense relationship with his mother begins to fray even more and his frustrations come to a head. John may not be a serial killer yet, but come the end credits, he certainly may be…

But, and with all due respect to Max Records, who plays young John Wayne Cleaver (really), few people will come away from I Am Not a Serial Killer talking about its central character. Enter Christopher Lloyd (really) as Bill Crowley (really), the old man who lives across the street and whose true nature you can probably guess already… to an extent.

Which is a shame, because what makes I Am Not a Serial Killer really interesting (yes, aside from Christopher Lloyd) is the fact that John actually isn’t a serial killer. Many such horror thrillers would have taken the core of the idea – baby would-be/could-be serial killer meets the real thing – and turned it into a banal, depressing piece about a serial killer in training, like Apt Pupil meets Henry: Portrait of a Serial Killer. But John is a wannabe serial killer who really doesn’t wanna be, turning the story into a game of cat and mouse between not only John and Bill but also the former and his own darkest desires. It’s reminiscent of the best seasons of Dexter crossed with a less oblique Hannibal. It’s curiously sweet and optimistic, even as John threatens to cut open a school bully like a cardboard box and pulls a knife on his own mother.

Okay, now we can talk about Christopher Lloyd. Obviously, the man is great, but he’s also genuinely surprising here. The film flirts with black comedy, but Lloyd plays it almost entirely straight, selling every aspect of Bill’s fractured personality, from kooky old neighbour to loving husband to ruthless serial killer. The mad, gurning Christopher Lloyd performance you may have expected from I Am Not a Serial Killer would have worked too, but the one we get should go down as the actor’s best role since Doc Brown in Back to the Future. Given how tremendously his horror/drama chops work out here, it’s as much a shame as it is impressive to see him tackle such a role so late in his career.

 This isn’t always backed up by the most believable storytelling though. One minute Bill is a weak and frail old man with heart problems and lungfuls of black gunk, the next he’s effortlessly dispatching men half his age and stalking incompetent police officers like a bona fide slasher villain. At least Tobin Bell’s Jigsaw had others do all of the hard work for him. The utterly left field finale explains such logical inconsistencies to an extent, but it doesn’t make these frequent moments of silliness feel any less frustrating.

Talking of silliness, there’s a slight devolution in that ending, the hitherto classy and thoughtful horror drama thriller turned on its head with an about face not dissimilar to if Heat suddenly became The Fast and the Furious for the ending. It still works, because Records and Lloyd are that good (hence the Heat comparison, see), and is apparently faithful to the novel upon which it is based, but some will be left less than enthused by the contrast between what the film could have been and what it ultimately becomes. But hey, at least it’s not predictable.

The ending and dafter slasher elements also rankle against the film’s carefully etched, low-fi, grainy look, which is more Snowtown than Dexter. Like Lloyd’s supporting performance, it’s chilly and understated, and almost dream-like in places. Not forgetting the soundtrack either, which is cool but low-key throughout, before bursting into something great for the end credits (visually great too, for what it’s worth) – which will leave fans with a big grin on their face and a swell in the heart (really).

To date, there are six books in the John Wayne Cleaver ‘trilogy’. On the basis of this adaptation of the first novel, I would be more than happy to see the young not-serial killer return. Heartfelt, intelligent and tricksy, whatever it ultimately may or may not turn out to be, I Am Not a Serial Killer is one of the best horror films of the year. Really.