Green Room is a divisive movie. Members of the audience I saw it with were shouting expletives and walking out in equal parts. It made my heart race and my palms sweat, and I had to do something I rarely do – keep telling myself it was only a movie because the immersion in a nightmare world was so real.

So yeah, it’s a little intense. It’s also a master class in suspense, a movie so stomach-churningly effective that the “white knuckle” descriptor actually applies. I was blown away by it and amazed that a movie could still affect me so jarringly. And while it’s ostensibly a crime movie/thriller, I don’t see how horror movies can compete with the tension (and gore!) that’s on screen in Green Room.

The central conceit is simple but writer-director Jeremy Saulnier proves once again (after last year’s stunning Blue Ruin) that the devil is in the details. Those details involve an idealistic punk band’s failing tour (siphoning gas and playing smalltown diners for $6 paydays) that leads them to take a remote gig in rural Oregon at a white supremecist club. Making up the band (“Ain’t Rights”) are: charismatic frontman Tiger (Callum Turner), level-headed bassist Pat (Anton Yelchin), lone female Sam (Alia Shawkat) and mercurial Reece (Joe Cole).

They walk into the viper’s den of skinheads with youthful bravado and no inkling of the situation that awaits them. They bait their neo-nazi crowd by starting their show with “Nazi Punks Fuck Off” by the Dead Kennedys, after which Tiger drolly observes “That was a cover.” They actually get through their set on the strength of their music, but it’s afterwards when things turn sour.

The mood that the film has built up to that point is one of pent up aggression and escalating tension. The heavily tattooed skinheads clearly have a propensity for violence that the moshpit only hinted at. After bursting into the green room (where bands kill time backstage) to retrieve an errant phone, the band witnesses the aftermath of a horrific act of violence perpetrated on Amber’s (Imogen Poots) friend. The skinheads quickly swerve into damage control mode and lock up Amber and Ain’t Rights in the green room while they scramble to determine next steps.

Once skinhead leader Darcy (a chilling Patrick Stewart playing against type) arrives and enlists the aid of his “red laces” (an elite skinhead force he’s created and a clear analogue for the nazi SS), the powder keg explodes in ways that are wholly unpredictable and shockingly, insanely grotesque. It starts with the band trying to exit the green room and a grievous injury against one of the members. The camera lingers on the wound and at this point its clear that Green Room is playing for keeps.

Once the skinheads bring in man-eating pitbulls  as mediators (their trainer intones “I’d consider it a personal favour if they died with meat in their teeth”) it’s evident that there’s no depths that Green Room won’t plumb to depict its living nightmare. Shotgun blasts, eviscerations, stabbings and worse are all depicted with clarity and a mounting level of suffocating dread. The characters themselves even comment on the situation, aware enough that their situation is dire and the chances for survival slim.

Probably the strongest element of the film is Saulnier’s mastery of tone and the push/pull frisson of explosive violence and exquisite suspense. You care enough about these characters (even though they’re quickly sketched) that the meat grinder they’re put through is all the more effective and affecting. Expectations are subverted at every turn so it’s never clear who will end up alive, which only adds to the “anything goes” vibe that the movie cultivates. There’s no room to catch your breath and by the end of it you’ll feel like you’ve been put through the wringer.

It may not have the thematic heft or strong characterization of Blue Ruin, but Green Room soars as a nasty thriller. The seige movie has rarely been done so well and with such technical proficiency, meaning there’s no real cracks in the foundation to reassure you that what’s happening isn’t real. For those who can stomach visceral gore and a descent into a nightmarish world, Green Room provides an unmatched level of nearly unbearable suspense. Watch it with an audience.

Green Room (2015)

Director: Jeremy Saulnier

Runtime: 94 minutes