Maude Gaillard, a psychologist, is found stabbed to death in her office. Florence Cassandre discovers that an unstable patient, Ida, fled shortly after a violent altercation. But the case gets more complicated: Delphine, the victim's sister, has reasons to want her gone, especially when it comes to a juicy inheritance. But the unexpected happens: while she's digging into these leads, Inspector Cassandre gets kidnapped! Could her abduction be linked to Maude's murder?