Kill List (18)

Starring: Neil Maskell, MyAnna Buring, Michael Smiley, Emma Fryer

Mysterious gaze: MyAnna Buring as Shel in the darkly enigmatic Kill List

Strong meat, this. Even those who cackled and cringed through Ben Wheatley's Brighton-based crime satire Down Terrace (also the best British picture of 2010), may find themselves recoiling at certain moments in his second film, Kill List. It's hard to say at present exactly what genre Wheatley is staking out, because his films never settle in one place. Mike Leigh was invoked by admirers of Down Terrace, though one could also detect notes of Ealing comedy at its darkest. The new one seems to establish the same mood of suburban malaise – "scatter cushions" get an early mention – before venturing into a more sinister realm which David Lynch, Harold Pinter and Wheatley's own namesake Dennis have stalked.

This time, the domestic unease centres on a couple with a young son. Jay (Neil Maskell) is a brawny ex-soldier who's still recovering from an unspecified trauma in Kiev eight months ago. His wife, Shel (MyAnna Buring), is not one to shirk a marital row, especially on the subject of their cashflow.

A dinner to which Jay's army mate Gal (Michael Smiley) has brought a new girlfriend, Fiona (Emma Fryer), simmers and then boils over into a screaming match between the hosts. Later, sensing his moment, Gal urges Jay to accept a lucrative job – their line of business, post-army, being contract murder. So, at an anonymous hotel they meet a close-mouthed client (Struan Rodger) who hands them the "kill list" of three targets. It seems straightforward, but turns out anything but.

A mystery story lies in wait, though Wheatley and his co-writer Amy Jump are as interested in the manner as the matter of their two killers. The script, as with Down Terrace, melds a precise vernacular with deadpan (and often chucklesome) improvisation by the actors. Maskell's Jay is a hair-trigger merchant with something dead behind the eyes; Smiley's Gal has a quicker intelligence and an Ulster charm not yet extinguished by his professional ruthlessness. There's a very funny scene early on when the pair are trying to have a quiet dinner in a hotel restaurant despite the staff having placed them adjacent to the only other occupied table (why do restaurants do that?). Jay is already seething when one of the company brings out a guitar and they launch into a jolly rendering of "Onward, Christian Soldiers". He walks over, snatches the instrument away and delivers some warning words, to which the guitarist quaveringly replies, "God's love can be hard to swallow." "Not as hard as a dinner plate," says Jay.

Mostly, the pair's talk comes in a knowing, side-of-the-mouth fashion that eludes almost everyone else. When Gal flirts with a hotel receptionist, she looks up distracted from fiddling with the PIN machine. "Sorry?" she says. "You won't be, love, honestly," Gal leers back.

Their first hit turns out to be a priest, prefaced by a plain title card across the screen: THE PRIEST. It's when they do their next, a "librarian", that things start to go awry. Having discovered in the target's lock-up an atrocity exhibition of porn shocking even to them, Jay decides to go "off-list" and take out the whole ring. But as the brutality escalates, so does the bafflement. What is the occult symbol carved on the reverse of a bathroom mirror? What "oath" did the client mean when he cut Jay's hand on sealing their arrangement? Why do the murder victims all smile and seem to "thank" the killers?

These small details planted seemingly at random will bear bitter fruit later. For the present, all is enigmatic. "It doesn't feel wrong," muses Jay of their kill-list, "...they're bad people", though he and Gal become so spooked by the job that they try to bale prematurely. No dice. The client insists on its completion, which leads our hapless hitmen deep into the woods and an encounter straight out of a Gothic nightmare.

Wheatley has said in interview that he likes movies that surprise and confound him. He insists that the multiple strands of mystery in Kill List do make sense, even if they aren't immediately decipherable. "The information is there... lurking in the corners of frames. I think it's far more scary to be half told, than definitively told." Agreed, though I'm still at a loss to unpack this one satisfactorily. One of its most unfathomable wrinkles is the reference to Kiev, where it all fell apart for Jay – but what happened there? The sudden flips into the surreal might argue that Jay has hallucinated the whole experience from his remembered stress back then in "Kiev".

This is a more ambitious and complex film than Down Terrace, which stayed determinedly humdrum even during its violent denouement. (I can never think of Willow pattern dinner plates in the same way again.) You sense a film-maker trying to raise the stakes, to draw out psychological and even political implications from a seemingly narrow story of professional murder.

The last hit on the list is an MP, yet in a gruesome twist there proves to be another – "the hunchback" – whose identity supplies the film with its hideous reveal. Hideous, though not as shocking as it might have been: last year's A Serbian Film got there first. It should secure the film cult status nonetheless, just as Edward Woodward's fate in The Wicker Man or Donald Sutherland's in Don't Look Now did for a previous generation. You will be asking yourself questions about Kill List once it's over, pondering its layers of meaning and its trail of clues. Of how many other recent British films could one say the same?