Inspector Lise Tanquerelle is under stress, as she often is, and is speeding through the streets of Paris when a cyclist suddenly comes towards her. Lise brakes too late and knocks the man down. As luck would have it, the cyclist is her childhood sweetheart Antoine Lemercier. Single mum Lise and the single professor of Greek history arrange to meet that very evening. But the rendezvous is short-lived, as the detective is called to a crime scene. A member of the National Assembly has been stabbed to death in cold blood and Lise is asked to take on the case. Lise, who is passionate about her job, tries to reconcile everything: Her child, Antoine and the murder case. But her next meetings with the professor are also interrupted by phone calls from police colleagues. She tries to keep her profession a secret from Antoine, who, like many of his academic friends, hates the authorities. The unsolved murder develops into a series of murders. Two other deputies are executed in the same way. But there is no trace of the perpetrator. Inspector Lise, who is taken off the case due to a lack of results, finds something in common between the three victims: They all have the same lover. Does this lead to the murderer?
—Arte