Leaving the Palais Garnier where he had just dropped off his daughter for her dance class, Raymond Sittler is assaulted on the steps of the Opera. A few seconds later, he starts convulsing, collapses on the porch and dies. Initially suspected, his mistress is also murdered at the Barbès-Rochechouart station, through poison. The investigation leads Jo to the prestigious Sorbonne University and to the door of a troubled student and his ambitious girlfriend.