In their quest for fame, The Relentless, a diverse rock band with members from both England and the US, find themselves captivated by the vibrant atmosphere of Los Angeles. At the center of this whirlwind is the charismatic vocalist, Johnny Faust, who grapples with the choice between his modest life in Columbus, Ohio, alongside his mother and girlfriend, Gretchen, and the seductive allure of stardom. As the band auditions for a new bassist, they are introduced to Lily, an exceptionally talented musician eager to join their journey.
A pivotal moment occurs when Johnny encounters a homeless man who offers sage advice about trusting one’s intuition rather than mere perception, setting the stage for an unsettling deal proposed by an enigmatic figure claiming to embody evil. This mysterious individual guarantees fame for The Relentless, but at a terrifying price: a human sacrifice. This dark proposition forces the band members to confront their moral convictions.
Amidst the chaos, Lily reveals her haunting history involving the cruelty of her former bandmate, Damien, deepening her bond with Johnny. However, tragedy strikes as Johnny learns of his mother's battle with breast cancer, further complicating his emotional turmoil. The tension escalates when a confrontation with Damien leads the band down a devastating path, resulting in a heart-wrenching decision to abandon their former bandmate. Tragically, when Johnny hesitates, Damien suffers a fatal fate as he attempts to flee the inferno.
With a record deal secured and their album American Satan released, The Relentless embarks on a nationwide tour that turns sour after a violent altercation in a Kansas bar. Following Johnny's arrest and subsequent acquittal, the band becomes perceived as harbingers of chaos. Their fans, emboldened by Johnny’s bravery, inadvertently initiate a series of tragic events that reflect the repercussions of their fame.
Struggling with the strains of a long-distance relationship, Johnny finds solace in substance abuse as Lily's increasing influence within the band leads to friction. Personal demons resurface as band member Ricky succumbs to a cocaine overdose while Leo drowns his sorrows in drugs. Heartbreak ensues when Gretchen decides to part ways with Johnny, who seeks comfort in heroin and Lily. The fallout is catastrophic, including the tragic fate of a teenager, manipulated by Johnny under dire circumstances.
As these events unfold, Johnny battles addiction and the burden of notoriety. Just when he believes he has hit rock bottom, the homeless man from earlier reappears as a harbinger of reality checks. In a bid for redemption, Johnny enters rehab while Lily disappears into obscurity. Despite the turmoil, American Satan skyrockets to the top of the charts, and The Relentless gains acclaim, their music resonating through a world that both idolizes and vilifies them.
While savoring their newfound success, a miracle occurs when Johnny's mother responds positively to cancer treatment, leading to her remission. Yet, unresolved issues haunt Johnny who futilely tries to reignite his romance with Gretchen, only to receive rejection once more. The band's appearance at a music festival takes a dark turn when the Devil, in an ominous guise, demands a human sacrifice during their performance.
As the moment unfolds, Lily makes a surprise return, followed by the appearance of the Devil manifested as Johnny’s mother's new partner. Seizing the crucial moment, Johnny confronts the Devil, briefly aiming a gun at himself before redirecting it toward the malevolent entity, effectively ending its sinister influence. His impulsive action provokes an immediate response from authorities who arrest him.
During his time in prison, Johnny is unexpectedly visited by Gabriel, the archangel, who was none other than the homeless man from before, and Gretchen, who still harbors deep feelings for him. Together with Damien’s father, an experienced lawyer, Gretchen plays an instrumental role in securing Johnny's release on a technicality. This pivotal moment allows Johnny to reclaim his future, making him confront the ramifications of his past actions and the crossroads that lie before him.
