In a bleak valley in Northern Italy, the River Po is swollen to its limits. The thick fog that usually clings to the town, blurring its surroundings and plunging its inhabitants into near-blindness, has been driven out by the raging storm. So when an empty barge drifts downriver, the fact the owner is missing does not go unnoticed. That same night Commissario Soneri is called in to investigate the murder of the boatman's brother. The brothers served together in the fascist militia fifty years earlier - could this be a revenge killing after so long?
Soneri's investigation meets with a wall of silence from those who make their living along the banks of river. As the fog descends and the valley is hidden once more, Soneri must navigate fifty-year-old loyalties and deep-rooted rivalries before he can find out the truth.