Original title "Meurtres en pays d'Oleron." Oleron is an island off the middle west coast of France, which seems to specialize in growing oysters - certainly the murders in this revolve around an oyster farm.
Our two heroes are the very thorny police captain Judith Valeix (Hélèlene Seuzaret) and the grumpy forensic specialist Vincent Lazare (Michel Cymès). Both are good at their jobs, but neither is particularly good with people. Valeix is also dealing with having moved to the area recently to live with her mother, who has cancer. And now they're faced with a series of murders, carefully placed and marked by the murderer.
Not bad, but not one of the better movies in the series.