On an early April afternoon, a bomb goes off in the Islamic Cooperation Council’s offices in Oslo, killing twenty-three people. The Police and Security Service suspect an extremist organization to be responsible for the attack, a suspicion that grows stronger when threats of yet another, bigger explosion during the planned celebration of the Norwegian constitution reach the authorities. As a special adviser on cold cases, Hanne Wilhelmsen has cut all of her official ties to the Security Service and lives contentedly—or at least as contentedly as someone like her can manage—in solitude with her partner Nesir and their young daughter. A small computer monitor is Hanne's only window to the outside until the day of the attacks, when her closed-off world is broken open. Hanne is approached by her long lost friend, Billy T., whose son Linus has undergone some disturbing changes recently. As the mood of the city darkens, Hanne tries to help Billy T. reach out to Linus and realizes that Oslo is up against forces far more terrible and menacing than ever before.