The drama follows two police officers who are sent to Fortitude, a fictional settlement in Arctic Norway, to help its citizens fight off dark and supernatural forces.
Richard Dormer returns as Sheriff Dan Anderson, who still suffers the effects of parasitic wasps from series one.
Anderson (Dormer) struggles to retain his emotional personality and his grip on reality.
Following on from series two, citizens of Fortitude rally around to protect both the town and Anderson from an outside investigation into the lynching of governor Erling Munk.