Following the brutal murder of an elderly man at Reykjavik’s harbour, ambitious but frustrated police detective Katrín Gunnarsdóttir is tasked with tracking down the killer.
Arnar Böðvarsson is brought in from Stockholm to help Reykjavik Police to investigate the murders, now suspected to be the work of a serial killer. The police turn their attention to the wayward son of one victim and search for a connection to the other.
An elderly woman is found dead at Valhalla children’s home and it seems to be the same killer. The police struggle to find the reason for the murders, but a witness offers a much-needed lead. Arnar scours a video for clues while Kata grows concerned for her son.
When it turns out that Valhall’s last employee is still alive, Kata and Arnar fear that the serial killer may find him before them and the police delve deeper into the dark history of the boys home. Arnar suffers a loss and Kata crosses a line. Meanwhile, public pressure to solve the murders grows stronger following a televised interview.
Kata and Arnar believe that they are finally on the trail of the serial killer, but the investigation takes them in an unexpected direction. Difficulties in their private lives take their toll, and a leak to the press puts both the investigation and lives in jeopardy.
After the Valhalla case is seemingly wrapped up, Arnar learns of several odd inconsistencies regarding one of the murders. Kata has a hard time letting go of things while ghosts from Arnar’s past return to haunt him.
As new evidence points them down a dark path, Kata and Hakon make a bold request from their superiors. Arnar tries to help but is consumed by his past and begins to rethink his family.
With the heinous truth about Valhalla out in the open, those responsible take drastic measures in an attempt to avoid detection. Kata is determined to deliver justice, but there are obstacles to overcome.