On a warm Autumn afternoon, Tivoli Gardens - Denmark's largest amusement park - is devastated by a terrorist attack. 1,241 people are killed. The unknown bomber is blown to bits; the security forces have no leads.

One year later, the nation is still reeling, and those behind the attack are still at large. Amidst the increasingly frustrated police force, Superintendent Lene Jensen is suffering the effects of tragedy closer to home. Everyone is aware the terrorists may soon strike again.

Then Lene receives a strange call. A young desperate Muslim woman needs her help, but by the time Lene reaches her she's already dead - supposedly suicide. Already suspicious, Lene's initial investigations suggest that the woman was unknowingly part of a secret services research project.

Silenced by her superiors, Lene turns to her old ally Michael Sander to dig deeper. But with even her allies increasingly adamant her actions are a risk to national security, Lene begins to understand that finding the truth might be the most dangerous thing of all.