In the harsh interior of the Finnish wilderness, best friends Aina and Siiri are inseparable despite their opposite natures: Aina is gentle and cautious while Siiri is headstrong and brave. But their friendship is put to the test when Aina is kidnapped by a death goddess and taken to the mythical underworld Tuonela.

Determined to save her friend, Siiri embarks on a dangerous journey north to seek out Väinämöinen, the only mystical shaman to travel to Tuonela and return alive. As the dark winter looms, Siiri uses all the strength she possesses to survive her journey, which is plagued by trappers, a band of roving wolves, and a cunning snow witch with her own quest for power. But finding Väinämöinen is only the beginning. Siiri must convince him to share his magic so she can sneak into Tuonela and save Aina.

In Tuonela, Aina is forced to play the sadistic games of Tuonetar, the cruel queen of the underworld, alongside other captured maidens. But Aina's kindness allows her to make allies in the dark, harsh environment. She soon discovers that Tuoni, the god of death and king of Tuonela, is also a victim of Tuonetar's spells that can only be broken when he remarries. To save him and the other girls, Aina offers herself as his bride.

As she spends more time in the underworld, Aina falls in love with Tuoni and must make a decision that will alter the course of her fate forever . . . not knowing her fearless friend is on the way and plotting a daring escape.