A young geneticist was stabbed in the Paris Catacombs, a Satanist symbol etched on her back. 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 skeletons of the catacombs. The trail leads to a mysterious woman who could well be a serial killer on the run. She seems to already have chosen her next victims: the family of a prominent politician. The killer turns out to be Nicole Wallace (played by Olivia d'Abo), the one-time nemesis of Det. Robert Goren in the series Law & Order: Criminal Intent (also created by René Balcer).