High-flying financiers are being murdered and it is beginning to appear like the work of a serial killer, prompting the formation of a special police unit.

Three businessmen are murdered on consecutive nights, sending the financial world into a panic and putting the A-Unit under immense pressure.

A Unit continues to hunt for the Kentucky Killer, the infamous American serial killer who is now on the loose in Sweden. The FBI are called in to help with the investigation.

While vacationing in the Netherlands, a Swedish family is killed by a car bomb and it's up to the A-Unit to solve the case.

When an illegal African immigrant is shot and killed by police, Kerstin Holm is assigned the task of interviewing the police officer. He happens to be her ex-boyfriend Dag Lundmark, who then disappears without a trace during the investigation.

The A-Unit has its hands full when celebrated Jewish neuroscientist Leonard Sheinkman is found murdered, strung up from a tree in a Jewish cemetery; a group of women escape from an immigration board hostel, where they are being exploited as prostitutes, and flee the country; and a body is found half eaten in the wolverine enclosure of a Stockholm zoo.

Recriminations threaten to split the A Unit apart, while the killer strikes again.

Ida is frustrated at how tantalisingly close the team came to saving the abducted girl.

Stockholm is rocked by an explosion on an underground train. When A Unit begins investigating, they uncover a fascist gang with ties to far-right groups all across Europe and its leader becomes their prime suspect. Kerstin is struggling to come to terms with the death of Bengt and her working relationship with Paul suffers as a result.

In their search for the bombers of an underground train, 'A' Unit has uncovered a fascist gang with links to terrorists across Europe. But as their net tightens around the suspects, another survivor emerges from a hiding place in the tunnel with information that will take the investigation in surprising new directions.