A woman is found murdered in her bathtub, and the murder made to look like a suicide. But a strange symbol found at the crime scene leads the local police to call Commissaire Adamsberg. When the symbol is found near the body of a second disguised suicide, a pattern starts to emerge: both victims were involved in a tragic incident in Iceland over 10 years ago. How are the deaths linked to the local Robespierre society? And what does the mysterious symbol signify?