1986. Caterina is a young teacher from Cefalù. She is happy with her life. She is passionate about her work as a teacher, she is happily married to Salvatore, a small antiquarian, and has a 13-year-old son, Luca, a lively and well-mannered boy. But one day her quiet routine is interrupted by a summons from the court of Palermo. She was drawn as a juror of the Maxi trial, held by the judges Falcone and Borsellino. It was the first time in history that the Italian State brought to the bar killers and mafia leaders, accused of forming a criminal association called Cosa Nostra under the control of a vertex called Cupola. Caterina is taken aback, it is a burdensome and also dangerous commitment. However, convinced by the judges and supported by her husband, she accepts. And her life is turned upside down. She must leave work and go to the bunker classroom in Palermo every day to attend the hearings. She sees ruthless people who are responsible for hundreds of murders, mobsters and ordinary people parading in front of her. It is an experience that deeply shocks her. But above all, it is her private life that is no longer the same. Her son Luca, feeling neglected, becomes aggressive and hostile. Her husband's shop is vandalized by the mafia and he asks her to leave the trial and go back to her old life. Caterina is frightened, torn, about to give in, but she resists. Thanks to the support of Giordano and Grasso, judges of the trial, the friendship of Rita, another juror, and the repentance of her husband and son, who in the end understand that she is doing the right thing, Caterina remains in her seat until the end, taking part in the council chamber which will establish, on December 1987, very heavy penalties for the accused. A terrible blow for the Sicilian mafia, to which Caterina contributed, with her civic sense and her courage.