Make no mistake, Kill List will haunt you. Forget about what you think you know about domestic drama, thrillers, and horror – for this is a story that is both all of those things and something completely different. When Jay, a middle-aged and domestically caged father, decides to take on one last job as a hitman, the task appears to be intense, but manageable. But the chain reaction that follows Jay’s monstrous errand spirals from merely dark to pitch black, where madness causes the nightmares to cross over into reality.

The tale begins with a domestic argument over money. Jay (the ever-intense Neil Maskell) hasn’t worked in months, and his wife Shel (a breathtaking MyAnna Buring) has turned the issue into a screaming battle. In the background, their seven-year-old son, Sam (Harry Simpson) frets – unsettled by the furor of the argument. The couple must regroup – for they are having Jay’s best friend, Gal (Michael Smiley), and his date over for dinner. When Jay loses his temper and destroys the dinner table – Gal follows him into the garage to offer him a devil’s deal. Turns out Gal is Jay’s old business partner, and, unzipping a bag full of guns, offers him one last lucrative hit job that could solve all of his troubles.

From here the film switches genres from domestic drama to dark thriller. And audiences might think they will know what kind of film to expect from here on out. They are wrong. From the moment they meet their menacing client (Struan Rodger), tantalizing hints are dropped about Jay’s past, including mention of a previous job in Kiev that Jay somehow botched. The client lays out three targets for the job – and Jay and Gal are off to do their fiendish business. By the way the first target is handled, it seems that Jay and Gal are more than up to the task. But as the killing starts, Jay becomes more and more deranged. The tantrums Jay displayed earlier morph into sadistic and violent tendencies, unsettling even his battle-hardened partner.

Indeed, the film’s tone reflects the unpredictability of Jay’s bipolar psyche. Masterfully played by Neil Maskell, the mood swings wildly between the violent menace of the job and hilarious banter with his partner. One moment he is doting on his son and lovingly holding his wife, the next he demonstrates new and horrifying uses for the common hammer. As soon as the story finds its center, it then throws it into violent orbit. The result is disorienting and scary, even for a thriller.

Before they know it, audiences find themselves switching genres yet again, to full-blown horror. How did the story end up here? What is going on? The questions swirl faster than the tics of Jay’s unstable brain. What happened in Kiev? Who is the client? Who are the targets, and why are they marked for death? What’s the deal with Gal’s mysterious girlfriend? And how much of it all is just in Jay’s head?

As the questions increase, so does the darkness. The unknown factors swirl and combine to form the worst kind of nightmare, where nothing makes sense and everything is threatening. Certain details seem significant, but it is uncertain what they mean. A cut on the hand. An unlucky rabbit. A mysterious tape. Gal’s creepy girlfriend. And the weird knife-scratched symbol.

The shocking conclusion leads one to rethink everything that has happened since the beginning. This is the kind of film that people will be talking about for years – because the mysteries are open to interpretation. It is not for the squeamish, and likely to give even serious horror fans surprises they haven’t experienced before.

Kill List never settles into the mere pedestrian, and for that it should be commended. At one point, Jay says to Gal, “We should do this more often.”

“What, kill rich people?”

“Yeah,” Jay replies, as they both laugh. Somehow, it feels like their targets did something heinous to deserve their fate. But the same must be true of the hitmen. Empathizing with evil is risky business, and may cause audiences a few of their own nightmares. If you can handle the thrill, it’s definitely worth it.