The film opens on July 21, 2011, just a day before the tragic events that would unfold. On that fateful day, Anders Behring Breivik (Anders Danielsen Lie), dressed in a police uniform, fills a van with homemade explosives and drives to Regjeringskvartalet, the executive government quarter situated in Oslo, Norway. He parks the van outside the office of Prime Minister Jens Stoltenberg (Ola G. Furuseth), and, moments later, the vehicle detonates, resulting in a devastating blast that leaves numerous casualties in its wake.
Meanwhile, on the island of Utøya in Tyrifjorden, Buskerud, a group of teenagers gathers for a summer camp organized by the Workers' Youth League (AUF), affiliated with the ruling Labour Party. As the news of the bombing reaches the camp, all festivities come to an abrupt halt. Among the campers, Viljar Hanssen (Jonas Strand Gravli) anxiously calls his parents to ensure their safety.
Breivik arrives at the ferry landing claiming to be a police officer dispatched to secure the island following the initial attack. He is transported to Utøya by the camp director, after which he orders the staff to corral the children in one area. When challenged for identification by the head of security, Breivik responds with violence, fatally shooting him and the director. Chaos erupts as the terrified children attempt to flee while Breivik fires indiscriminately, resulting in the tragic loss of dozens of lives.
As destruction reigns, Viljar and his brother, Torje Hanssen (Isak Bakli Aglen), take cover on a rocky beach alongside other students. Viljar manages to contact his mother, revealing the harrowing situation as the shooting unfolds. Breivik discovers their hiding spot and opens fire, leaving Viljar severely injured while Torje miraculously escapes unharmed. Subsequently, Breivik surrenders to police tactical teams and is taken for interrogation.
Viljar endures emergency surgery at the hospital to remove bullet fragments embedded within his brain, as danger looms over his recovery. His parents arrive at the camp, searching for Torje but soon become distraught when they learn that Viljar is missing. The mother, Christin Kristoffersen (Maria Bock), desperately tries to get updates from the hospital until she receives news that Viljar is undergoing critical surgery. Meanwhile, the father, Sveinn Are Hanssen (Thorbjørn Harr), grapples with the tragic knowledge that Viljar's best friends, Simon and Anders, have not survived the massacre.
During the subsequent interrogation, Breivik presents himself as the pro-Nazi leader of a white nationalist group called the Knight's Templar, threatening future attacks on command. He seeks legal representation from Geir Lippestad (Jon Øigarden), who faces an ethical dilemma in defending a client whose actions have caused immense sorrow. Lippestad contemplates an insanity defense, despite the backlash it garners, which could lead to Breivik's institutionalization rather than imprisonment. With expertise from several psychiatrists, Breivik is possibly diagnosed with paranoid schizophrenia. He expresses a desire to be deemed competent, wishing to validate his actions and face trial. Ultimately, it is revealed during the trial that Breivik took the lives of 77 individuals—8 in the initial Oslo bombing and 69 on Utøya.
After waking from a coma with life-altering injuries, Viljar discovers the impossibility of removing all bullet fragments from his brain, as some have settled perilously close to the brain stem. This reality leaves him burdened with uncertainty about his health and future. Furthermore, he loses sight in one eye and, upon returning home with his family, embarks on the arduous journey of rehabilitation. Though his mother endlessly supports him, the haunting memories of the massacre continue to plague him.
In a courageous act, along with another survivor named Lara Rachid (Seda Witt), Viljar testifies in court, recounting the horrifying details of the attack, including the heartbreaking losses of his best friends. Eventually, Breivik is convicted of murder and terrorism, receiving a life sentence in solitary confinement at Skien Prison, with the possibility of parole in 21 years—a chance that may ultimately result in him serving a life term behind bars. Intriguingly, despite his sentence, Breivik maintains a disturbing sense of pride.
As time passes, Viljar turns his focus toward his education, aspiring to become a lawyer and pursue a career in politics, while Lippestad remains a dedicated practitioner of law in Oslo. Jens Stoltenberg continues in his role as Prime Minister until 2013, after which he ascends to the position of Secretary General of NATO.
