Under the rubble of a fresco that collapsed from the ceiling of an old chapel in Alsace, a man’s body is found. The chapel has long belonged to a religious community, whose members call themselves the Messengers of the Lord. In essence, it’s a closed sect living by its own laws—laws going back into the depths of time. They shun modern gadgets and other achievements of civilization. They dress like it’s the 18th century, pray, grow grapes, and make wine famous across all of Europe.
The dead man was one of the leaders of the community. However, the police have doubts that his death was the result of an accident. The investigation brings in Pierre Niémant and his young assistant, Ivana Bohdanovich. While Niémant, with help from local gendarmes, searches for clues, Ivana infiltrates the ranks of vineyard workers in order to observe the strange community from the inside during the grape harvest.
Meanwhile, the situation escalates and new victims appear. But the search for the killer won’t move forward until investigators answer two questions: where did a piece of coal come from in the dead man’s mouth, and what do the hidden frescoes found beneath the paintings on the ceiling of the gloomy chapel mean?