The weapon in this gripping and gruesome punk rock horror-thriller are many and various.
Guns, machetes, box cutters, attack dogs and fire extinguishers are all unleashed as a band tries to fight its way to survival after being held hostage in a backwoods club by the American Nazi skinheads who run the place.
But the movie's best weapon? Feedback. That is, the screechy sound of distressed speakers, which here becomes rock 'n' roll pest control. It's just one of director-writer Jeremy Saulnier's inventive touches to a movie in which he slam-dances together slasher-flick moves with a palpable punk-rock energy.
Yes, it's a grim affair. And it's one that, after its engaging set-up, eventually makes you care less about the characters' chances of survival as the body count inevitably spirals upward.
Though the ending is never predictable. And with Saulnier racking up the tension and claustrophobia, and some ferocious performances from its cast, Green Room is an electrifying genre-bending blast.
Among the riveting turns are the late Anton Yelchin (from the Star Trek movies) as the mild-mannered bassist in struggling punk quartet The Ain't Rights, which we find is touring the toilets of the Pacific Northwest.
The score a rare paying gig at a white supremacist hang-out in outback Oregon.
But having survived playing The Dead Kennedys' Nazi Punk F*** Off to the boots 'n' braces crowd, they stumble backstage on something they shouldn't have.
Soon, a stand-off between the club's heavies and the panicking group, barricaded in the green room, has turned into something resembling Night of the Evil Dead with skinheads and their pooches substituting for rampaging zombies.
Also memorable is Imogen Poots, as a skinhead girlfriend forced to pick sides in the mayhem in which she has also become an accidental participant. Her character provides some of the movie's most shockingly violent moments, and its noisiest too - she's the one who discovers a practical use for howling feedback.
The best performance, though, comes from another former Starship Enterprise-er.
Patrick Stewart is certainly follicly qualified as skinhead leader Darcy. But the unnerving calm and tactical wisdom he and Saulnier's script bring to the nasty neo-Nazi mob boss makes him all the more engaging than if he was just another KKK nutter.
He helps make Green Room something smarter than just a punk rock reinvention of Deliverance.
Cast: Patrick Stewart, Anton Yelchin, Imogen Poots, Alia Shawkat, Joe Cole, Callum Turner, Mark Webber, Eric Edelstein
Director: Jeremy Saulnier
Rating: R18 (Graphic violence, drug use and offensive language)
Running time: 95 mins
Verdict: Riveting rock killing spree