In 15th century Bologna, Italy, Jews are prohibited, under penalty of death, from becoming locksmiths. Lovely young widow, Avisa Baglatoni, befriends a young Jewish lad, Bernardo. Her life and those of her loved ones are in peril because the mayor's nephew, Ippolito, desires Avisa and suspects Bernardo is not what he seems.

A glib orator comes to Bologna and the city responds by collecting silver for the city's bells. When the city's treasure is stolen beneath the noses of the assembled dignitaries, Duke Henri Bentivoglio swears vengeance.

All of Avisa's locksmithing skills and courage are required to save her life and those she loves.