In the basement of a remote cabin, Finnish police officer Nina Kautsalo uncovers a horrifying discovery. The find quickly draws the attention of German virologist Thomas Lorenz, who is soon brought in to assist with the investigation.

With the National Bureau of Investigation joining the inquiry, Nina found herself removed from the case. Yet, a fresh discovery offered a glimmer of hope: tracks in the snow, promising a new avenue of pursuit.

Raunola, the suspect in the murders, continues to confound the investigators. The viral outbreak investigation takes a troubling turn, and Nina and Thomas unexpectedly cross paths.

The investigations into both the criminal matter and the outbreak proceed with a frustrating slowness. For Nina and Thomas, the boundaries between their professional and private lives are beginning to blur.

The investigation into the virus deepens with each passing day. Authorities have now located the fourth person affected.

Nina is afforded the opportunity to question the fourth woman. Meanwhile, Esko finds himself in difficulty with law enforcement. The first victim stirs from a prolonged state of unconsciousness.

The return of Raunola to Ivalo casts a shadow of peril over Nina and Thomas. Meanwhile, Marita receives unwelcome tidings while under quarantine.

A surprising source delivers new information to Nina and Thomas. Thomas now faces a difficult battle for custody of his daughter. A viral infection takes a chilling turn.

Nina and Thomas embarked on an unauthorized journey to Murmansk. Meanwhile, Venla struggled desperately for survival.

Nina and Thomas journey back to Finland. Venla finds assistance from an unlikely quarter. Nina will once again be compelled to confront the shadows.