NOTE: This spoiler was submitted by Evan B

The female member of a rock band (Jenny Ortega) crawls down a hallway in a palatial home. She begs for her life as a man pursues her. The rocker looks to her side to find another bandmate dead with his face split open. The pursuer catches up and bashes the rocker’s head in with a hammer.

Jumping ahead in time, the Foo Fighters (a famous rock band) are meeting with their manager Shill (Jeff Garlin) to discuss their 10th album. Front man Dave Grohl (himself) is suffering from a musical block, unable to think of any new songs. Shill is not empathetic, saying that he has debts to pay and therefore the Foo Fighters need to make a new record ASAP. Grohl says that he wants to try something different than recording in a studio in order to get him past his block. Shill contacts a property manager named Barb Weems (Leslie Grossman) to rent a house for them that will help the band find inspiration.

The band – including Dave Grohl, guitarists Chris “Shiff” Shiflett and Pat Smear, bassist Nate Mendel, keyboardist Rami Jaffee, and drummer Taylor Hawkins (all played by themselves) – arrive at the mansion from the beginning of the film. Weems shows them around the property and Grohl has psychic visions of the slaughter depicted at the beginning of the film. Liking the atmosphere (and influenced by the supernatural), Grohl convinces the band to stay and record at the house. While setting up equipment, one of the crew members dies in an electrical accident caused by a spectral being. But Grohl convinces the band to continue recording at the house in his honor. However, Grohl remains uninspired, even trying to rip off a song made by another artist (cameo by Lionel Richie). They also meet next-door neighbor Samantha (Whitney Cummings), who tries to befriend the band.

One night, after Grohl has demon-plagued nightmares, he awakens and follows a figure moving through the woods. He is led to a decrepit basement structure. Inside, Grohl finds a dead raccoon split open and nailed to the wall above a drain. He also finds an audio recording from a band called Dream Widow (shown being killed at the beginning). He plays the recording and rocks out. However, the recording suddenly plays backward on its own and Grohl is possessed by an unseen spirit.

The next morning, Grohl summons the band and plays an amazing guitar solo. He claims to have invented a new musical key (the key of “L”) and gets the band to have a productive rehearsal. Grohl dismisses the crew (cameo by John Carpenter) so that the band can continue recording on their own. That night, Grohl blows off a delivery guy (Will Forte) who has his own band and idolizes the Foo Fighters.

The Foo Fighters continue to record and the band members try to cater to Grohl’s increasingly fickle demands. When Samantha drops off cocaine-infused lemon bars, she warns the band that murders occurred in the house. Grohl orders some groceries and the delivery guy is killed (decapitated with hedge clippers) when he follows demonic figures into the woods while making the delivery. That night, Grohl eats his steak raw, much to the band’s disgust.

As time passes, the song they are recording goes over 30 minutes. Weems visits and finds the house in a filthy condition and the band reaching their breaking point with Grohl. Eventually, Shiff angrily confronts Grohl before leaving rehearsal to grill some lunch. While grilling, Grohl sneaks up behind him and kills him by burning him to death on the grill. Meanwhile, Hawkins finds the delivery guy’s disemboweled and beheaded corpse. The band wants to call the police, but Grohl confiscates their phones and car keys and demands they finish the song (now in honor of the delivery guy).

The band decides to meet secretly to discuss Shiff’s disappearance and what to do about Grohl and the song (which is now over 40 minutes). They ask Samantha about the house’s history. She reveals that she was a groupie for the Dream Widow band. She explains that the band (and Samantha herself) began dabbling in the dark arts in order to enhance their music and that the mansion is located atop a portal between Earth and Hell. The Dream Widow front man found a cursed book that was activated by sacrificial blood (the front man used raccoon blood) to commune with demons. The demons eventually possessed the front man in an effort to record a hellish rock song. The front man killed his band while possessed, but then killed himself to prevent the song from being finished. She says (and the band agrees) that the same demon is now possessing Dave Grohl. Smear and Mendel go to find the book (as it contains an exorcism spell), Hawkins is sent to distract the now demonic-looking Grohl, and Rami and Samantha go off to have sex. Grohl kills Rami and Samantha mid-coitus (chainsawing the pair in half while hiding under the bed), and then finishes recording the song with Hawkins before killing him too (throwing a cymbal through Hawkins’ face). He also eats Shiff’s body (as demons crave human flesh).

Smear and Mendel find the cursed book hidden under the drain beneath the dead raccoon carcas. They are accosted by demons, but manage to escape. Grohl pursues his remaining bandmates, but they manage to complete the exorcism spell to break the possession. Grohl pukes out the spirit of the Dream Widow front man. Grohl then beats up the demonic front man before the spirits of the Dream Widow band drag their front man to Hell where he can be tortured.

As Smear, Mendel and Grohl walk to their van to leave the house, they are confronted by Shill and Weems. It turns out that the pair are satan worshippers that set everything up. Smear and Mendel try to hotwire the car so they can escape while Grohl fights Shill. Unfortunately, Weems confronts the bandmates and all three die in the ensuing struggle (Smear’s head is crushed under the van’s tires, Weems is fatally struck by the van, and Weems stabs Mendel through the head with a knife before she dies). Grohl almost manages to kill Shill, but stops when Shill begins laughing at the realization that the band completed the song. Shill notes that this song will save Rock and Roll and that it’s time for Dave Grohl to be a solo act.

The film jumps ahead one year to a Dave Grohl solo concert. An excited crowd chants his name. As Grohl prepares to go onstage to perform the demonic song, his eyes turn black (showing that he is now permanently possessed by evil).

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When he reads from a cursed book, Foo Fighter frontman Dave Grohl is possessed by a demon that wants to bring a Hellish rock song into existence. The Foo Fighters complete the song before possessed Dave Grohl kills most of the band members. Although the remaining band members tried to exorcise Grohl before they are killed off by their Satan-worshipping manager, it is unsuccessful as the finished song keeps Grohl possessed forever. The demonic Dave Grohl becomes a wildly successful solo act.