Set in the 1970s, Blackwater tells the story of how four random people's lives converge after two tourists are found murdered in a tent near the Swedish mountain town of Blackwater.
A young gang member is found dead, and the Beck group's investigation indicates that a drug network is behind it. Klas Fredén has been monitoring the network for a long time, and the Beck group - led by Alex Beijer - is most graciously allowed to work with the murder investigation in parallel. She will soon end up on a collision course with Fredén. Thus, Martin Beck, who is now head of department, is also involved in the case.