In 1987, a young guitarist, Euronymous, establishes the groundbreaking black metal band Mayhem in Norway, teaming up with bassist Necrobutcher and drummer Manheim. However, after Manheim departs, they bring in new drummer Hellhammer. The band soon recruits a Swedish vocalist named Dead, whose erratic and self-destructive behavior creates a notorious image; during performances, he cuts himself, showers blood on the audience, and hurls pig heads at those he terms "posers."
At a particular performance captured by their friend Metalion, the band meets a fan, Kristian, whom Euronymous initially dismisses. Tragedy strikes when Dead, in a fit of despair, takes his own life by slitting his wrists and throat, followed by a gunshot to his head using Euronymous' shotgun. Rather than alert the authorities, Euronymous imprudently poses and photographs Dead’s body, even making morbid necklaces from pieces of his skull to distribute among the band members. This callous display results in Necrobutcher walking away from the band in disgust.
Euronymous then launches his own black metal label and opens a record store named Helvete ("Hell"), which evolves into a gathering place for fans and musicians, including Fenriz from Darkthrone, Faust from Emperor, and Kristian, who has now adopted the name Varg Vikernes. They collectively earn the title of the "Black Circle." Tensions rise when Varg, in rebellion against Euronymous, sets fire to a local church. In a retaliatory act, Euronymous, joined by Varg and Faust, also burns down a church, solidifying their infamous reputation.
Euronymous enlists Varg as Mayhem's bassist alongside guitarist Blackthorn and Hungarian vocalist Attila Csihar to create their first album, De Mysteriis Dom Sathanas. A power struggle brews between Euronymous and Varg, eventually leading to a series of church arsons and the shocking murder of a gay man by Faust, prompting the police to investigate connections to the black metal scene. As Helvete shuts its doors, Varg—now the prime suspect in the crimes—makes a boastful admission of guilt in an interview, although he is initially released due to insufficient evidence.
With growing tension, Varg informs Euronymous of his intention to leave the band to start his own record label. In retaliation, Euronymous reveals that the skull necklaces were indeed fake and declares that his violent persona is merely an act, sparking Varg's outrage. While cleaning up the store, Euronymous vents his frustrations about Varg, even expressing thoughts of murder. Once he calms down, he sends Varg a contract for their music rights.
Upon learning of Euronymous' death threats, Varg travels to Oslo under the pretense of signing the contract. Once allowed inside, the situation escalates, and Varg brutally stabs Euronymous after a brief exchange. The attack continues in the stairwell, where Varg cruelly continues stabbing Euronymous, ignoring his pleas for mercy. Following the news of Euronymous' murder, Varg is arrested and eventually convicted not only of the murder but also for participating in the church burnings, receiving a maximum sentence of 21 years.
In a poignant voice-over, Euronymous reflects on his life, urging the audience not to grieve for him, emphasizing the successes and achievements he has accomplished.
