On an early April afternoon, a bomb goes off in the Oslo offices of the National Council for Islam in Norway, killing 23 people. The police and security service suspect an extremist organization to be responsible for the attack, a suspicion that grows stronger when threats reach authorities of a bigger explosion planned for the celebration of the Norwegian constitution.

As a special advisor on cold cases, Hanne Wilhelmsen has cut her official ties to the Security Service and lives contentedly - or at least as contentedly as she can manage - in solitude with her partner, Nefis, 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 recently undergone some disturbing changes. 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.