The legend of the Breton island says: if a murder occurs here, then blood appears on the stone slabs of ancient monuments. Celtic tales? This has been believed for many centuries. But now the legend is turning into a terrible reality. The island is shaken again and again by cruel, inexplicable murders - and the blood of each new victim stains the ancient menhirs and dolmens. Perhaps the crimes are of a ritual nature? The experienced Parisian investigator Fersen is sure of this. However, Captain Marie Kermer, who once lived here, who joined the investigation, is convinced: the murders are connected with the centuries-old enmity of three local aristocratic families, which neither time nor distance can calm down. Has the old war really resumed? But then mortal danger loomed over Marie herself, the heiress of one of the warring clans...