 Strozzi, the chief of a mercenary army, kills the banker Chigi, because the man refused to let him marry his daughter Berta, who is engaged to Giuliano de  Medici. Giuliano is accused of the murder, he is arrested and imprisoned to be tried. Strozzi, who feels very confident about Giuliano s trial, confesses to Giuliano s brother, the Cardinal Giovanni, he is the real killer. Giovanni cannot plead the innocence of his brother because he cannot reveal what he learned during the Holy Confession. Giuliano is sentenced to death. With a trick, on the day of the execution, Giovanni is able to make Strozzi reveal his crime, while witnesses are secretly listening to them. The truth is finally established and the guilty soldier finally faces his destiny.