Finnish police Nina Kautsalo makes a horrific discovery in the basement of wilderness cabin. Soon the find brings German virologist, Thomas Lorenz, to work on the case.

National Bureau of Investigation joins the investigation and Nina is forced off the case. Tracks in the snow give her a new lead, however.

Raunola, the man suspected for the murders is leaving the investigators confused. The virus investigation takes a bad turn, and Nina and Thomas find each other in surprising place.

Both crime and virus investigations are progressing slowly. Work and personal life are starting to mix for both Nina and Thomas.

Virus investigation becomes even more topical. Police track down the fourth victim.

Nina gets a chance to interrogate the fourth woman. Esko gets into trouble with the police. The first victim wakes up from coma.

Nina and Thomas are in danger when Raunola returns to Ivalo. Marita gets bad news in quarantine.

Nina and Thomas get new information from a surprising source. Thomas has to fight for his daughter's custody. Virus infection takes a frightening turn.

Nina and Thomas return to Finland. Venla gets help from unexpected source. Nina will have to step into the darkness once more.