Leonardo has completed his super-weapon,which he hopes will be used as a deterrent to dissuade the Milanese from war. De Medici however intends to take it to war and kill Rocco. With war imminent all Milanese are considered undesirable aliens and Alberto,cousin to De Medici's right hand man Placidi,is charged with rounding them up. Leonardo helps Lucia and her grandmother Carla,accused of being Milanese spies,to escape Florence whilst implicating Alberto as a double agent. The mob get Alberto but Placidi escapes. De Medici,aware that he knows too much about the duke's murder,allows the mob to claim Placidi too but,as he lies at death's door,he is spotted by Leonardo. He decides to tell the young artist something important.