When retired policeman Herbert Molin is found brutally slaughtered on his remote farm in the northern forests of Sweden, police find strange tracks in the snow, as if someone had been practicing the tango. Stefan Lindman, a young police officer recently diagnosed with mouth cancer, decides to investigate the murder of his former colleague but is soon enmeshed in a mystifying case with no witnesses and no apparent motives. Terrified of the disease that could take his life, Lindman becomes more and more reckless as he unearths the chilling links between Molin's death and an underground neo-Nazi network that runs further and deeper than he could ever have imagined.