An elderly woman is found dead in her bathroom. The police could conclude that it is a suicide if there wasn't a strange symbol engraved next to her body, resembling a guillotine. Two days later, a wealthy scientist is found dead in his office. All the evidence would point to suicide again, if it wasn't for the same symbol engraved next to him. The police, led by inspectors Antamberg and Danglar, are faced with a dark case that, as Antamberg describes it, is "a bucket of seaweed". Along the way, it will be revealed that the two victims share a common secret, an old trip to Iceland where a terrible tragedy occurred, and both frequented an original and strange society with a theme of the French Revolution... As time passes and other members of this society are murdered, always with the symbol of the guillotine hidden nearby. What is the real purpose of the existence of this society, led by François Sato, a chillingly faithful replica of Robespierre, and what connects these successive murders with that tragic trip to Iceland?

With her characteristic skill, which combines paradox with reality and escalating suspense with an almost cynical humor, Fred Vargas signs an exceptional novel of "suspense and action".