To go by the book and the locations, it is about two murders in the fishing business in the extreme west of Brittany around the bay of Douarnenez. A fisherwoman is found with her throat slit next to the fish auctioning hall in Douarnenez. Just as Commissaire Dupin and his team start questioning locals, a second murder is reported from the small island of Sein. The first victim hails from there, was known for her sustainable opinions and opposition to the local fishing magnate. The second victim is a biologist who just recently moved there. She was occupied with studying the dolphins in Iroise Maritime Nature Park.