Green Room is about a punk band called the Ain’t Rights as Pat, Sam, Reece, and Tiger travel through the Pacific Northwest. When their gig gets cancelled in Portland, a local radio host named Tad gets them a new one at a neo-Nazi skinhead bar his cousin, Daniel, works at. It’s a shady place located in the woods outside Portland.
The show goes fine, but once they head out, Pat returns to the green room to pickup Sam’s phone. Inside, he sees the body of a girl named Emily. One of the neo-Nazis stabbed her to death.
Pat goes to call the police, but two bar employees Gabe and Big Justin stop him. They take everyone’s phones, and lock them as hostages in the green room.
Gabe pays one skinhead to stab another to make the death look like self defense. The bar’s owner is also the skinheads leader named Darcy. He’s says they need to kill the band to eliminate witnesses.
The band manages to overpower Big Justin, and then hold him hostage with a boxcutter and pistol they take off him. Darcy negotiates with them through the door, and asks them to hand over the pistol. Pat agrees, but when he opens the door, Emily’s friend Amber screams it’s a trap.
Darcy and his men grab his arm, and hack at it with machetes until he drops the gun. Pat is able to close the door though. Big Justin takes the opportunity to attack the band, but Reece chokes him unconscious. When Big Justin wakes again, Reece chokes him down again, and Amber kills him with the boxcutter.
As the band looks for a way out, they find an underground drug lab. However, its only exit is locked from the outside. They arm themselves with anything that can be used as a weapon, and exit the green room where they find the club empty. The neo-Nazi, Clark, has a big dog he unleashes, and it kills Tiger. Amber and Pat use microphone feedback to drive the dog away. Reece tries to escape jumping out a window, but a skinhead hacks him to death.
Pat, Amber, and Sam retreat back to the green room. Darcy sends Daniel into the club to kill the remaining band members in retaliation for killing Emily. Amber lets Daniel know that another neo-Nazi named Werm murdered Emily when he discovered Daniel and Emily were planning to leave the skinheads.
Daniel then agrees to help them escape, and he leads the band into the club. The club’s bartender shoots him dead. The group kills the bartender for their bit of repayment, and they then take his shotgun. Clark’s dog is back, and it kills Sam. Darcy’s men then wound Amber, who returns back to the green room with Pat.
Next, Darcy sends Jonathan and Kyle to kill Pat and Amber. He then walks away with the bodies to make their their deaths to appear as if they were killed trespassing. Pat lures Jonathan down into the drug lab while Kyle remains back in the green room. Amber kills Kyle with a boxcutter to the throat. Pat and Jonathan fight, but Amber sneaks up from behind, and shoots him. As Gabe enters the green room, he finds his buddies dead, so he surrenders to Pat and Amber.
They hold Gabe at gunpoint, and trek through the woods. Pat finds Darcy and his men staging the crime scene, so he and Amber go to take them out. Meanwhile, Gabe volunteers to go to a nearby farm to call the police. Pat and Amber then kill Clark and Alan. Darcy pulls a gun from his jacket, but Pat and Amber kill him dead too. Exhausted, they then sit on the side of the road, and wait for the police as the film ends.