Place Des Vosges, a stones throw from Victor Hugo's apartment. A young woman is found dead from a blunt-force head wound. Jo deducts the murder was not premeditated, but maybe a crime of passion, maybe the result of a struggle an argument gone bad. She is identified as Marie-Eve Lambert, a small-time art dealer from the Paris banlieue. Her husband professes not to know what she was doing in the Marais at night. He has an alibi, though his general demeanor rubs Jo the wrong way. Maybe she was meeting a lover?

A young woman is found stabbed to death in the Catacombs. Since some parts of the Catacombs are a known hang-out for Goth teenagers and would-be Satanists, suspicion at first falls on those two groups. But the style of the killing suggests a sexual motive. The victim is identified as a DNA researcher in a lab, a repressed loner whose life under closer examination reveals that she frequented sex bondage clubs - the police thinks that maybe she was in the Catacombs for a sexual rendezvous. While the rest of his team is chasing the sex angle, Jo links the dead girl to some missing lab equipment - equipment he learns is used to insert DNA into living cells.