At the convent, Isabella learns the rules of her order and expresses her desire to live under "strict restraint." Lucio arrives at the convent and Isabella is sent to speak with him, because she has not yet taken her vows, which prohibit the sisters from speaking with men. Lucio reveals that he is seeking Isabella on behalf of her "unhappy brother," Claudio. When Isabella asks him what the problem is, Lucio tells her forthrightly that her brother is in prison for impregnating a woman.
Here, Isabella is introduced as a character so pure that she actively exiles herself from the immorality of Viennese society. Her desire for “strict restraint” reflects a devotion to orthodoxy that will clash with her devotion to Claudio, who is being disciplined for violating precisely the doctrine that Isabella venerates.
Initially, Isabella tells Lucio to stop making fun of her with false stories. Lucio responds that while it’s true that he is partial to deceiving maidens, Isabella's innocence and purity compels him to speak to her sincerely, as he would to a saint. He then reveals that Juliet, Isabella's friend, is the woman Claudio has impregnated. When Isabella asks why the couple does not marry, Lucio tells her that they would, however Duke has been temporarily replaced by cold, cerebral Angelo. Claudio is to be made into an example and executed, and Lucio asks Isabella to endeavor to "soften" Angelo in the hopes he may pardon her brother. Isabella promises she will do so straightaway.
Even the mischievous and licentious Lucio is deferential towards Isabella’s innocence and purity. At this point, Isabella’s religious devotion does not seriously conflict with her love for Claudio—she is quick to leave her nunnery and reenter the unsheltered world in order to help her brother.