Without knowing the identity of an American serial killer who's on a plane flying from New York City to Stockholm, the A-Unit tries to find him.

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.

Continuing their probe into the car bombing leads the A-Unit to a shady celebrity restaurateur and a Dutch drug-smuggling ring.

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.

A Unit discovers a link between the shooting of an illegal African immigrant, bodies found in a marsh in Varmland and an apparent suicide. Kerstin Holm tries to track down missing police officer Dag Lundmark single-handedly. Suddenly she realises that he has come across a terrible secret and is just waiting for her to find him.

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.

When Söderstedt is sent to Italy in pursuit of leads linked to the wolverine killing, he crosses paths with a treacherous Mafia boss. Soon he finds himself in Germany following up leads from the murdered Leonard Sheinkman's war diaries, while also trying to unravel the mystery of the inheritance he has received from his uncle.

The A Unit is rapidly reunited to trace an assassin targeting Polish women in hiding in Sweden, but new recruit Ida struggles to fit in, while former member Paul Hjelm's personal dilemmas cloud his work at Internal Affairs.

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

Kerstin is caught up in a murderous bank robbery by two Russians, but a third man's participation proves puzzling.

The A Unit investigation suggests a Cold War connection. Past secrets worth killing for are revealed as team members pursue the elusive men behind the crime.

A Swedish biker gang's link to sex trafficking two teen girls to Belgium means A Unit is already on the case when a another young blonde goes missing. Paul Hjelm investigates a claim against a vice squad officer.

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.

A woman is found collapsed in the street, having escaped from an unknown basement. She has no idea why she was kidnapped and, with nothing else to go on, 'A' Unit follows a lead found in the basement to a drugs ring run by two brothers.

Investigating a series of murders and kidnaps, 'A' Unit begins to suspect they are linked to a shared high school experience - but this still isn't getting them any closer to catching the killer. Paul is investigating the sudden and mysterious death of his new-found friend from the security service.

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

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.