It’s been eight months since professional assassin Jay (Neil Maskell) has booked a job. After a disastrous outing in Kiev, it doesn’t seem like anyone is willing to take a chance on him, and as talented as he is it is beginning to look like he might never work again. His wife Shel (MyAnna Buring), a former Army Special Forces operative herself he spent some time in Afghanistan, is tired of her husband’s constant moping. He’s got a family to support, and with medical bills piling up and a young son to feed she needs him to find some work and fast.

Neil Maskell in Kill List © IFC Films

When his former partner Gal (Michael Smiley) comes over for dinner with a new girlfriend (Emma Fryer) in tow and a new multi-target assignment in his pocket, Jay is hardly in the position to turn him down. Together, the two set out to finish off a list of targets as handed to them by a mysterious benefactor, and while each one seemingly deserves to be done in their calm happiness at having Jay pull the trigger is a bewildering shock. As thing progress, the hitman becomes convinced something sinister is at play here, something that potentially could put both Shel and his son in harm’s way. But the list must be finished, there is no turning back from that, and the closer Jay comes to silencing the last target the more clear it becomes he’s been the one under the microscope all along.

I have to admit, co-writer and director Ben Wheatley’s Kill List is a sly and altogether unsettling follow-up to his relatively successful Down Terrace. At first looking as if it is going to play in that same underworld milieu of a mid-level crime family trying to make ends meet, the movie subtly begins to morph its way into becoming something completely different, delivering an unnerving climax that is uncompromising as it is unnerving. In some ways a slickly conceived combining of Stephen Frears’ The Hit and Robin Hardy’s The Wicker Man (the one with Edward Woodward, not Nicolas Cage), this devious little thriller is a horrific sojourn into the unknown making the finished product a genre-bending sensation sure to perplex just as many viewer as it delights.

Color me in that latter crowd, because after about 30 minutes Wheatley had me completely under his thumb slowly burrowing me deeper and deeper into my seat. He pokes and prods the audience, tilts at them sideways, he and fellow writer Amy Jump going out of their way to make things as obtuse and as weird as possible yet somehow always maintain focus on character and narrative at the same time. It’s a neat trick, and one that’s pretty darn successful for most of the film’s modest running time, and while the eventual outcome isn’t as shocking as I’m sure the pair hoped it would be I was still unsettled enough by what I saw to leave all the lights on in my small apartment for a good hour after it had ended.

What I liked most about the pair’s script is how the clues for what is happening and for what is about to take place are nicely littered throughout. Some are obvious – Gal’s date ominously retiring to the bathroom to carve some sort of symbol on the back of Jay and Shel’s mirror – while others take a little more doing to make out. But for the most part they are all there, and by the time a sinister cult of Pagan-like semi-naked (or, in some cases, completely naked) worshipers appear the impact is more freaky and disturbing than it is a surprise.

The movie does take a little bit of time to find its footing, and the opening scenes between Jay and Shel are moderately annoying and I wasn’t sure I was in the mood to spend 90-plus minutes of my time dealing with them. But these scenes of marital discord are vitally important to the events to come, making the impact of the last scene all the more devastating.

Wheatley is quickly becoming a director to keep an eye on. The way he is able to bend genres, his gift with setting atmosphere and his ability to not let a moderately quick pace strip anything away from the development of the characters are all outstanding. Kill List isn’t an easy film to categorize, to put into a mass market boss general audiences can easily recognize. At the same time, it gets the job done and then some, and as an excursion into debilitating emotional-based familial terror I doubt we’ll see its like throughout the rest of 2012.

• Kill List Theatrical Trailer