Vincentio, disguised as Friar Lodowick, arrives at Saint Luke’s which is where Mariana, Angelo’s spurned lover, resides. Mariana, who has been singing, greets Friar Lodowick and apologizes for seeming to be happy, explaining that she sings to cope with her grief. Friar Loddowick greets Mariana, telling her she need not apologize. He asks if anyone has arrived asking for him. Mariana says no. By and by, Isabel appears. Excusing himself from Mariana a moment, Friar Loddowick takes Isabel aside and asks if Angelo has agreed to the terms of the proposed tryst. Isabel says that Angelo has. She explains that Mariana’s incognito presence will be understood to be Isabel’s servant who is there to attend to her brother. Satisfied, Friar Lodowick introduces Mariana to Isabel and has Isabel explain to Mariana their devious but just plan. Mariana consents to do her part.
The Provost presents a proposal to Pompey: Help Abhorson, the executioner, with the business of executing the condemned and he--Pompey--will be set free; otherwise Pompey will serve out the entire term of his imprisonment. Pompey accepts the proposal and is directly introduced to Abhorson. Abhorson is told not to stand on ceremony as Pompey is a bawd. Reluctantly, Abhorson undertakes the task of training Pompey. They are told to go and tell Claudio and Barnardine to appear before the Provost. Presently, Claudio appears. He is shown the official edict authorizing his execution: Claudio is to die by tomorrow morning. When asked of Barnardine’s whereabouts, Claudio says he is asleep, oblivious of his impending death. Claudio is dismissed. Vincentio, disguised as Friar Lodowick, arrives and asks the Provost if anyone has arrived before him. The Provost says no. Just then there is a knocking which the Provost goes to answer. When he returns, Friar Lodowick asks the Provost if it's not a message from Angelo, commuting Claudio’s execution. The Provost is certain that it is anything but. By and by, Angelo’s messenger arrives with a letter. The Provost reads the letter. The letter says that the Provost is to expedite Claudio’s execution by four in the morning and to show Angelo Claudio’s head by five in the morning.
So the plan hasn’t fallen through, which means that it must be improvised.
Friar Lodowick inquires about Barnardine, the other man who is slated to be executed tomorrow. The Provost says that Barnardine has practically grown up in prison, that he refuses to leave prison even with the threat of his execution hanging over his head, that he is perpetually drunk and cares not if he is alive or dead. This gives Friar Lodowick an idea. It would require the Provost’s cooperation, however, which Friar Lodowick garners by showing the Provost the Duke’s hand and seal, his signet, proving thereby that Friar Lodowick is acting as the Duke’s emissary.What Friar Lodowick would have the Provost do is to execute Barnardine in Claudio’s place and present Angelo with Banardine’s head, having shaved and altered Barnardine’s head and beard for disguise.
On account of old, familiar faces inhabiting the prison, faces he was wont to see frequent Mistress Overdone’s house of ill-repute, Pompey can’t help but to think that working as Mistress Overdone’s assistant and working as Abhorson’s assistant are one and the same when he is ordered to summon Barnardine. Barnardine is reluctant to answer the summons, however, and when he answers eventually, he does it only to tell his executioners that he is drunk and that he will not consent to die in the state that he is in. Indeed, even Friar Lodowick’s efforts to convince Barnardine otherwise proves futile.
The Provost has an idea. Earlier in the day, Ragozine, a pirate who bears a closer resemblance to Claudio than Barnardine to Claudio, had died of a fever. What if they present Angelo with Ragozine’s head? Friar Lodowick approves of the plan. As to Claudio and Barnardine, Friar Lodowick tells the Provost to remove them to a remote area of the prison, giving the impression, however temporarily, that they have been executed and their bodies disposed of. By and by, Isabel arrives to confirm that her brother’s sentence has been commuted. Friar Lodowick decides to withhold the truth for now, telling Isabel that their plan has failed, and that Claudio has been executed. Understandably, Isabel becomes visibly upset. She would like nothing better than to pluck out Angelo’s eyes. But Friar Lodowick pacifies her, telling her of the Duke’s imminent return, of Angelo’s subsequent reckoning, and Isabel’s redress. He tells her to go to Friar Peter and inform him of Friar Lodowick’s wish to hold a conference wherein they will find way to find redress for both Isabel and Mariana. Friar Lodowick then tells Isabel that after his conference with Friar Peter he himself must attend to a religious duty which will keep him busy and away. He is about to leave the city when Lucio arrives on the scene and insists on escorting Friar Lodowick to the city limits.
Angelo is in a state of worry and doubt as a letter has arrived from the Duke, ordering a strange procedure wherein petitioners vis-à-vis the state will have an opportunity to air their grievances in public.
Friar Lodowick, divested of his friar’s robe, enters Vienna with Friar Peter. He gives Friar Peter instructions on what to do when they are soon to meet again but for now to get Flavius. Presently, the Duke is met by one of the his trusted men, Varrius.
Isabel confides in Mariana as to how, as instructed by Friar Peter, she is to tone down her petition vis-a-vis Angelo, saying how if she had her druthers she would prefer not to when Friar Peter arrives. He is to take them where the Duke is presently making his public appearance.