Three best friends embark on a road trip to a heavy-metal show, where they bond with three aspiring musicians and head off to one of the girls’ country home for an after-party.
In the 80’s a trio of friends – Alexis, Val, and Bev – meet another trio of guys – Mark, Kovacs, and Ivan – at a heavy metal concert. The girls invite the guys to Alexis’s family’s house where they reveal themselves to be part of a religious fanatic cult that has been killing people they view as heathens and making it look like a satanic cult were the culprits.
Alexis kills Ivan before Mark and Kovacs free themselves and hide in the wine closet. Alexis’s stepmom comes by and had called the cops after seeing the guys’ van and thinking they were getting robbed. Alexis kills her after she sees Ivan’s corpse, and Val kills the sheriff after he goes inside the house.
Bev ends up turning on Alexis and Val after realizing how horrible they are and decides to help Mark and Kovacs. Alexis’s father, Pastor John Henry Butler, the leader of the cult, comes home and kills Kovacs before going to chastise Alexis for screwing up their plans. Bev fights Val and lights her hair on fire before knocking Butler unconscious. Alexis fights her but falls out a window. Bev goes to save Mark, but Alexis tries one last attempt to go after them before Bev runs her over.
Alexis is blamed for every recent killing while Butler never suffers any consequences. Bev and Mark drive away to get medical help.
In Indiana, July 1988, Alexis Butler and her two friends Val and Bev are driving to a heavy metal show, when a milkshake is thrown from a blue van onto their windshield. Once they get to the concert, they find the same blue van, and Val throws a small firecracker into it, causing the three boys inside to climb out. Ivan owns the van and his buddies Kovacs and Mark, who is said to be leaving for Los Angeles soon, are interested in the girls. After the show, Alexis invites the boys to her father’s empty mansion. Bev and Mark seem to like each other, yet Bev seems to almost avoid him. The girls drug the boys’ drinks and reveal they are going to murder them and make it look like a Satanic cult killing.
The Daughters of the Dawn, the church the girls are a part of, has murdered eighteen other people in the same way in order to create fear and send more people to their religion. Alexis is shown to be the most insane and stabs Ivan after he criticizes her religious belief in Christ, and he bleeds to death. Mark and Kovacs briefly escape, and the two boys hide in a pantry. Susan, Alexis’s soon-to-be ex-stepmother, comes home to retrieve a passport and reveals she has called the police because she saw the strange blue van and the house lights on. Susan then discovers Ivan’s body and Alexis stabs her to death.
A police officer arrives and becomes suspicious, so Alexis runs from him and back into the house where he chases her, gun raised. The officer finds the injured Kovacs and Mark who pleads for help but Val sneaks up on him, takes his gun, and shoots him, killing him. Alexis and Val fight over the gun, and Bev appears, threatening her friends with a chainsaw. Val and Alexis tell Bev they are doing the Lord’s work, but Bev declares she will let Mark and Kovacs go.
Bev tries to help Mark and Kovacs, the latter who is bleeding out and won’t last much longer unless he gets to a hospital. Alexis has the car keys, so Mark goes after her to retrieve them. When Kovacs sees car lights, he goes outside struggling to walk to find John Henry Butler, Alexis’s father and the pastor of the Daughters of the Dawn. Mark gets the keys, but Alexis attacks him and they fight. Val attacks Bev and tries to kill her, but Bev lights Val on fire (her hair being full of hairspray). Butler attacks Kovacs off-screen and he makes it back into the house where Bev finds him. Just before Kovacs dies, he tells Bev to save Mark.
Butler shoots Mark as he is strangling Alexis. He then berates his daughter for doing a terrible job murdering and covering it up. He tells Alexis they have to make some sacrifices to get out of the predicament she has caused and attempts to strangle her to death when Bev comes up and knocks him out. Alexis is over-the-top crazy and Bev throws her out of a window in a dramatic and exaggerated fashion. Mark is still alive, and he drives away with Bev, only to find Alexis standing in the road. Off-camera, Bev runs Alexis over.
Butler is still alive and makes himself into a victim, claiming that Alexis was led astray and joined a Satanic cult. Bev and Mark leave town together.
Indiana, 1988 – Friends Alexis (Alexandra Daddario), Valerie (Maddie Hasson), and Beverly (Amy Forsyth) are headed to a heavy metal concert for the band Soldiers of Satan. On the way there, they overhear a news report about a series of murders that appear to be the work of a satanic cult. Pastor John Henry Butler (Johnny Knoxville) discusses how music like heavy metal is to blame for these murders.
The girls have a chocolate milkshake thrown at their windshield before they arrive at the venue. Once there, they spot the van belonging to the guys who threw the shake. Val throws a firecracker in there as payback. The guys step out and apologize after the girls mention the milkshake. They introduce themselves as Mark (Keean Johnson), Ivan (Austin Swift), and Kovacs (Logan Miller). They agree to put it behind them and have drinks while watching the concert together.
The group enjoys the concert and then make plans to go back to Alexis’s home since her parents aren’t going to be there. Bev and Mark appear to have an attraction toward one another. Everyone gathers around a campfire for a game of “Never Have I Ever”. After a few playful rounds, Alexis admits that she drugged the guys. They think it’s a joke until they all start to gradually pass out.
The guys wake up half naked and tied up to chairs. The girls reveal that they are part of a group that commits murders as part of some kind of cycle that their group performs to kill others that supposedly worship Satan. Ivan calls them out on their bullshit which drives Alex to stab him in the throat, killing him. Before they can go ahead and kill the others, Bev stops them to pull the other girls aside to talk to them.
Bev tells Alexis and Val that she wants to go for the next kill. During this time, Mark and Kovacs free themselves and run inside the wine cellar to hide. Alexis slashes Kovacs’ arm and causes him to bleed profusely. Moments later, Alexis’s stepmom Susan (Allison McAtee) comes by because she forgot her passport for her upcoming trip. She mentions to Alexis that she called the cops because she saw the guys’ van and thought it was suspicious. While Alexis tries to hide this from Susan, she stumbles upon Ivan’s corpse. Before she can find out what’s going on, Alexis stabs her in the gut, and Susan bleeds to death.
Mark tends to Kovacs’s arm wound. While they try to find a way out, Sheriff Dembrowski (Tanner Beard) shows up to respond to Susan’s call. Alex tries to cover herself up, but Dembrowski makes his way inside to investigate. As he announces his presence, Mark and Kovacs try to explain that the girls are trying to kill them, but he tries to arrest them. Val takes his gun and shoots him dead. The guys run back inside the wine cellar as Val tries to shoot them before Alex tells them to stop wasting bullets.
Bev then comes out with a weed whacker to reveal she wants no part in the other girls’ scheme and plans to free the guys. She tells the girls that Butler, who is Alex’s father and is the leader of the cult, has been brainwashing them and funneling donations into his own accounts. Val attacks Bev until she gets slammed into the wall. In the struggle, the guys break free with broken wine bottles, and Kovacs lightly wounds Bev as they run for it. Mark realizes Bev is not with the other girls, just as Alexis and Val turn the lights off in the house.
As the three try to escape, Butler comes home and Kovacs tries to get his help. He sees Kovacs holding Dembrowski’s gun after Val lost it, and Butler shoots Kovacs. Meanwhile, Bev fights Val while Alexis attacks Mark. Butler shoots Mark in the side and tells Alexis she screwed everything up by drawing attention to their crimes. Bev gets Val off her by lighting her hair on fire (igniting the hair spray), and then finds Butler trying to choke Alexis. Bev hits him over the head and knocks him unconscious. Alexis tries to play victim before Bev fights her off, and Alexis trips over Mark’s arm, causing her to fall out the window. Bev helps Mark up, and he is distraught to find Kovacs dead.
Bev and Mark run to Alexis’s car to get away. Before they drive off, a not dead Alexis limps over to the road. Bev promptly runs her over.
Bev later stops at a convenience store for medical supplies where she sees a news report about the killings. They are blamed on Alexis and the cult, revealed to be named We Summon The Darkness. Butler pretends to be distraught at his daughter’s death and involvement in the crimes, but expresses optimism in things getting back on track. After paying, Bev tells the cashier to not believe everything he sees. She returns to the car to give the supplies to Mark, and they continue to drive off.