Plot summary

Jon Burroughs (Domhnall Gleeson) is an aspiring songwriter from England who struggles as he is lacking any artistic vision. One day while walking along the beach, he witnesses a man, later revealed to be named Lucas, trying to drown himself. As Lucas is taken to the hospital, Jon meets a man named Don (Scoot McNairy), who explains Lucas is a keyboardist in an experimental band called The Soronprfbs, of whom Don is the manager. Jon mentions that he plays keyboards and is invited to play with them that night. Jon goes along and meets the rest of the band - aggressive theremin player Clara (Maggie Gyllenhaal), French guitarist Baraque (Francois Civil), drummer Nana (Carla Azar), and leader and vocalist Frank (Michael Fassbender) - all of whom are eccentric and reluctant to accept Jon as an actual member, except Frank, who wears a papier-mâché mask at all times. Just as Jon is beginning to understand the band's sound, Clara is shocked by an electrical fault. When the other members stop playing to see if she's alright, she lashes out at them for doing so and storms offstage.Some time later, Frank invites Jon to become a permanent member with little to no explanation. He eagerly accepts and accompanies them to Ireland for what he initially believes to be a weekend gig, but is actually a year-long project to record their debut album in a remote cabin. Clara is very disdainful towards Jon, and continually belittles him for his mediocrity. One day, Don overhears Jon composing a song. He says that he, too, wanted to be a songwriter once but lacked any talent. He plays a song for Jon, who compliments it. Don tells Jon that Jon will eventually realize he can't be like Frank, because Frank is unique. The next day, Don reveals he has not paid the cabin's rent and that they are being evicted, but Jon offers to pay what is owed using his grandfather's inheritance. The morning after they complete recording of their album, Jon finds Frank's corpse hanging from a tree. He calls the rest of the band down and they remove the mask, only to discover it was Don wearing one of Frank's masks. Don is cremated and Clara tells Jon that Don was the band's first keyboard player.Afterwards, Jon reveals he has been secretly posting the band's recording sessions on social media. Because of this, The Soronprfbs have gained a small fan following and have been invited to perform at South by Southwest. The other members are offended at Jon's clandestine promotion of the band, but Frank is excited by the prospect of a large audience and agrees to go to the festival. Later, while Jon is soaking in the hot tub, Clara angrily confronts him and accuses him of manipulating Frank and giving him delusions of grandeur. The ensuing argument culminates in them having angry sex, after which Clara tells Jon that he disgusts her and they will never be together again. Clara warns Jon that if things go badly in Austin she'll stab him.Upon arrival in Texas, The Soronprfbs scatter Don's ashes in the desert, but realize that Baraque accidentally packed a canister of powdered food instead of the ashes. When they make it to Austin and check in for the festival, they discover that they aren't as popular as they thought, and that most of the crowd will have never heard even heard of them. Upon hearing this, Frank starts to become erratic and has a panic attack. Clara realizes that Frank's fragile mental health has left him unequipped to handle these types of situations, so she pleads with Jon to help convince Frank to not perform and go back to their unknown status. Jon refuses and works with Frank to try to create versions of their songs that will appeal to a wider audience. On the day before the concert, Clara and Frank disappear. Jon finds them in an alley where Clara is trying to soothe Frank to stave off a mental breakdown. Focused on the show, Jon tries to get Frank to go back to the festival with him, but Clara stabs Jon in the leg as promised. She is subsequently arrested and Jon uses the scandal to build publicity for the band.Back at the hotel room Nana and Baraque reveal their disdain for Jon's selfish intentions and quit the band the night before the concert, refusing to perform without Clara. Jon and Frank decide to go on anyways as a duo. Jon tries opening the set with one of his own songs rather than a song from the band's album, causing Frank to suffer a nervous breakdown and collapse on stage, telling Jon that his music is "shit." The two are then forced to move into a cheap motel together. One day, a frustrated Jon attempts to reason with Frank and asks him to remove the mask - when he refuses, Jon tries to take it off using force. Frank panics and flees but is hit by a car, shattering the fake head. Jon pursues him, but Frank has escaped before Jon was able to see his real face, leaving only remains of the mask behind. Jon realizes he cannot identify Frank without the fake head. He subsequently gets hit by a car.After being released from the hospital, Jon goes to a diner. Another customer in the restaurant recognizes Jon from the videos online, and comments on his perceived "hilarity" of Frank's nervous breakdown and sudden disappearance and Clara's assault of Jon, referring to them as "freaks" and "wayward." It then dawns on Jon that their internet popularity was never about the music; their "fans" were simply ridiculing them for how strangely they all behaved. Sometime later, Jon has attempted to track down Frank in order to make amends, but he cannot be found anywhere. However, he finds a bar where Clara, Nana, and Baraque are now playing as a trio. He apologizes to them for taking control of the band. Jon finally succeeds in tracking Frank to his hometown of Bluff, Kansas, where he is living with his parents. Jon sees Frank's real face for the first time and discovers that he is scarred and balding from prolonged use of the mask. Frank's parents explain that he has had mental health issues all his life and began wearing the mask as a teenager after his dad made it for him for an alleged costume party. Jon assumes that Frank's artistic creativity is a result of the "torment" his mental illnesses have put him through or that he experienced some sort of traumatic event, but his parents deny this, affirming that Frank grew up in a loving home and that his mental health problems never propelled him, just limited him. Jon now understands that Frank's talent isn't from trauma or mental illness, but that Frank's genius was just inherent, and that he will never be able to be like him; just as Don had told him. Jon apologizes to Frank for ruining the band and trying to take off his mask. Frank admits that he has lost his artistic vision and finds himself unable to write songs ever since The Soronprfbs disbanded. He then takes Frank to the bar where the band is. Frank begins to speak and they realize who he is. He begins singing and joins them in a song while Jon leaves the bar.