Alexandre Bruce investigates with Martine Lewine. Paul Dark, the director of a scientific research laboratory, is found dead at home, poisoned by strychnine, a poison which causes horrible pain. The murderer photographed his agony and signed his crime in the victim’s blood : Cobra... At the same moment on the Seine, his ex-wife Ophélie Rex, an extremist artist, is assassinated while floating on an inflatable mattress and making a mythical communion with her namesake. Commissionner Serge Clémenti investigates the murder.