When three elderly men are poisoned, apparently by spider bites, everyone assumes that the deaths are tragic accidents. But at police headquarters in Paris, Inspector Adamsberg begins to suspect that the case is far more complex than first appears. It isn't long before Adamsberg is pursuing a series of rumours and allegations that take him to the south of France, and the shocking events that occurred at La Miséricorde orphanage, decades ago. A spate of serious injuries there was linked to bites from the same local species, the recluse spider. Adamsberg is convinced that, through the haunting crimes of the past, he can prove that the men were victims of an ingenious serial killer.