Duke Vincentio of Vienna plans to leave the city and appoints Lord Angelo as his deputy, instructing him to govern in his absence. He leaves him with a faithful old man named Escalus to assist him. Vincentio praises Angelo for being an upstanding and virtuous man, while Angelo expresses doubts about his own abilities until he has been tested. Vincentio leaves in secret, not wanting the people to applaud him as he departs.

Lucio, a young gentleman from Vienna, talks with two of his soldier companions about how they pray for war in order to fund their livelihood, just as pirates must ignore the biblical commandment “thou shalt not steal’ because they need theft in order to survive. The soldiers discuss the sexually transmitted infections they may have acquired from sex workers and Lucio mocks how this behavior has impacted their bodies.

Mistress Overdone, a brothel owner, tells the men that their friend Claudio has been arrested and taken to prison because he impregnated a woman named Juliet. Lucio goes to learn the truth. Mistress Overdone speaks with the brothel’s bartender, Pompey, complaining that the new governor has ordered that all of the brothels outside of the city limits be torn down and that she will have no way to make money.