Odd numbers

The novel is the ninth installment in the Hanne Wilhelmsen series. It follows detective Hanne Wilhelmsen as she investigates deadly bombings at the Islamic Cooperation Council's headquarters in Oslo, which kill twenty-three people. The police suspect an extremist organization. Hanne, working as a special adviser on cold cases, is drawn into the investigation when her former partner, Billy T., approaches her for help with his son, who has begun exhibiting disturbing changes and may be involved in the events.