A Finnish police officer discovers a dying Russian sex worker being held captive in a farm cellar, carrying a deadly virus. Meanwhile in Helsinki, the case comes to the attention of the European Center of Disease Control and its German virologist.
Authorities locate Raunola's snowmobile but he remains missing. Meanwhile, Nina is ordered to meet with Thomas and assist with the investigation into the Yemeni virus. As a result, all pregnant women in the area are ordered to get tested.
Nina tries to elicit a confession from Raunola for three murders, while Tomas continues testing pregnant women. However, when they try to test the women at an infamous 'prostitution bus,' they find themselves face-to-face with an uncooperative guard.
Nina and Thomas comb through the list of Marita's sexual partners and focus in on a peculiarity in the year 2012, which they are intent to ask her about. Meanwhile, in Russia, Raunola is captured by the mysterious Maxim.
A pregnant woman from a local religious Laestadian sect arrives at the health center but Thomas' attempt to deliver her baby results in tragic consequences. In Russia, Raunola agrees to help Cevikovic.
Irina is only willing to talk to Nina, as she opens up her past as a sex slave to a Russian oligarch and the events that brought her to Finland. But, after ratting out one of her former captors, Irina becomes terrified that he might be after her.
Nina arrives at Hamari's house, where she is surprised by Raunola. He ties her up, sets the house ablaze and leaves her to die, before he heads to the hospital to fulfill the mission Cevikovic gave him in Murmansk --- the murder of Irina.
A man named Marcus contacts Thomas and Nina to describe his reason for seeking revenge on Cevikovic. The incident he describes, which occurred during The Bosnian War, gives them insight into not only the virus but also Cevikovic's warped intentions.
Nina informs the strike team that they have a very small window to complete their task. As they infiltrate Cevikovic's alleged Russian address, they release they've walked straight into an ambush. At the hospital, Venla's condition gets worse.
Nina is unconscious after crashing her snowmobile. Thomas manages to pull her onto his but with angry Russian officials pursuing them, and his vehicle low on gas, he is desperate to cross the border back to Finland.
