A young geneticist was stabbed in the Catacombs. On his back is engraved a Satanist symbol. Jo is convinced that this is a crime of passion. But the case takes an unexpected turn when the team discovers that the victim was conducting experiments with plague bacteria recovered from the skeletons of the catacombs. The trail leads to a mysterious woman who could be a serial killer at large. It already seems to have chosen his next victim: the family of a politician first plan.