Kill List starts with a furious argument between husband and wife. We come forearmed with the knowledge that this is a British horror film. We don’t expect it to start with a family dispute, like some low budget kitchen sink drama, but all the shouting and swearing immediately unsettles. Before the movie even kicks into horror mode, (and it’s quite a while before it does, despite the odd moment of foreshadowing) the mood is disconcerting.

Jay and Shel are a married couple with a ten year old boy, living in a boxy, semi-detached in London. Jay has been unemployed for a year, and is slowly going mad at home. Jay’s best mate, laid back, humorous Irishman Gal, brings his new girlfriend, Fiona, around for dinner. The dinner party seems lifted from a Mike Leigh film, as the conversation becomes awkward and tensions ripple beneath the surface.

It is only during the dinner party that we get the first hint of the horror to come when Fiona visits the bathroom. With the door locked she takes a mirror off the wall and inscribes an occult symbol, featured on the posters and heavily throughout the film, onto the back.

Jay and Gal are army buddies, and there are plenty of allusions to a job in Kiev that went very wrong. But, like much else in this mysterious, downbeat film, the specifics of what are left unspoken. But Gal has a new job lined up, and he wants Jay in on it too. One they are both exceptionally suited to.

A kill list.

Now the film veers into hitman thriller territory, although the kitchen sink drama element still runs through the film’s veins. The two friends stay in bland hotels as they travel the country, and have very uncool, unTarantinoesque conversations about painters and decorators, and dirty soap.

The film’s bleak atmosphere is leavened occasionally by brief moments of humour, mainly provided by Gal, played by Michael Smiley from Spaced. My favourite moment is when Jay and Gal decide they have had enough and return to their employer to try and get out of the rest of the contract.

He refuses, and tells them that if they renege on the deal he will murder them, and then their families. Deadpan, Gal replies, “So, no wriggle room then?”

At Kill List’s heart is the wonderfully sketched out relationship between Jay and Gal. In one scene they scrap like schoolboys, and in another, one plants a tender kiss on the other’s forehead. Michael Smiley and Neil Maskell are both excellent in their roles.

I wish I could say more about the plot, but I would end up filling this review with spoilers. Of course the hits don’t go quite as planned, and our two protagonists slowly come to realise that there is more going on than they first realised, as the narrative charts a relentless, downbeat path towards a nasty, deeply unsettling ending.

This is the sort of film that stays with you long after it has finished. In the case of Kill List that finally becomes a weakness as, upon reflection, the story doesn’t quite tie together, and we are left with too many unanswered questions.

But don’t let that put you off. Kill List is the best horror film I have seen for a long time.