Isabella is one of the play’s main protagonists, and she is a veritable incarnation of steadfast virtue. So committed is she to a life of moral probity that she has decided to join a convent. However, she is prevented from pledging her vows when she’s notified that her brother, Claudio, has been arrested and sentenced to death for the crime of fornication. Isabella’s arc therefore carries her out of the convent and back into the world of sin she had desired to escape. It is back in the sinful city that Angelo propositions her to have sex in exchange for her brother’s pardon. Isabella righteously refuses Angelo’s proposition, and she further shows her virtue in her fastidious commitment not to sacrifice her chastity—and therefore her immortal soul—even when her brother asks her to do so. Yet for all her virtue, Isabella is arguably excessive in her sexual restraint, occupying the opposite side of the spectrum from her sexually unrestrained brother. From a certain perspective, her restraint may even be read as having psychosexual origins. Consider the language she uses to refuse Angelo:
[W]ere I under the terms of death,
Th’ impression of keen whips I’d wear as rubies
And strip myself to death as to a bed
That longing have been sick for, ere I’d yield
My body up to shame. (2.4.107–111)
These words have a sadomasochistic undertone that suggests Isabella might derive pleasure from her rigorous refusal of the flesh.
Despite being a main character, it isn’t entirely clear if or how Isabella changes over the course of the play. For much of the action she is in fact constrained by the directives of men. Initially it’s Lucio that tells her to go plead with Angelo for Claudio’s life. Then Claudio tells her she should save his life by denying herself. Finally, the Duke—disguised as a friar—swoops in and involves her in his elaborate plan. But even though the Duke ultimately aims to liberate Isabella from the tangled mess of desire and sin, he essentially treats her as a pawn in his own game. He manipulates her into doing as he wishes, but without filling her in on the full extent of his plot. He even goes so far as to convince her that her brother has been executed, likely to ensure that she’ll deliver a genuine performance when she lodges an official complaint against Angelo in the last act. In these ways, Isabella is a pawn in a patriarchal system that at once relies on and dismisses women. That said, at the play's end, we may read Isabella’s failure—refusal?—to respond to the Duke’s marriage proposal as her way of silently reasserting her agency.