Lucia goes to Monza, to a convent, while Renzo heads to Milan, where he becomes involved in a popular unrest (caused by lack of bread).

Lucia is kidnapped by a rich man, a friend of Don Rodrigo, after a female nun (of noble descent) at the convent is coerced into helping.

Lucia is brought to the castle of the Innominato (Nameless), a friend of Don Rodrigo, but he has second thoughts about his cruel action.

He decides to set Lucia free, accompanied by the parish priest Don Abbondio, who is subsequently rebuked for his moral weakness.

When Renzo finally finds and embraces Lucia, the two can at last get married (despite a vow she'd made to the contrary), because they are no longer oppressed.