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.

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.