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. A group of tourists found themselves trapped on a deserted island for two weeks, surrounded by thick, impenetrable fog, and two of them didn't make it back alive. But how are the deaths linked to the local Robespierre society? And what does the mysterious symbol signify?