As a young girl, Hildur Rúnarsdóttir experienced the heart-wrenching disappearance of her two little sisters. Now she works as a police officer in the western fjords of Iceland. As Hildur investigates a perplexing series of crimes, she unexpectedly receives support from two trainee officers, Finnish Jakob Johanson and German Florian Hermann. While apprehending the serial killer, the old mystery begins to unravel, and Hildur must confront the truth about her sisters.