Prospero, in Act 1, Scene 2, gives a long speech to his daughter Miranda telling how, 12 years ago, he was deposed as Duke of Milan to this island by his evil brother Antonio. Prospero and the theme of the wielding of power, in four roles: as ruler, as magician, as artist (creator of theatrical illusions), and as educator.

The four romances at the end of Shakespeare’s career, belonging to an age-old genre, the tale of wonders and marvels, from the Wanderings of the Odyssey to fantasy and science fiction in our time. Act 1, scene one. Why try to stage a storm at sea? A touchstone: how various people face imminent death.

The Duke returns and passes judgment. Mariana pleads for Angelo, wanting him despite his faults. Remarkably, Isabella pleads for Angelo. Four possible weddings: Angelo and Mariana, Isabella and the Duke, Claudio and Julietta, Lucio and the prostitute he got pregnant. A happy ending? The double meaning of “measure for measure,” according to justice or to mercy.

The Duke’s plan to fool Angelo by substituting the head of Barnardine won’t work because Barnardine humorously refuses to be hanged. So they substitute the head of an already dead criminal for Claudio’s. The Duke “returns” in Act 5. Isabella and Mariana accuse Angelo but are arrested for slander. Lucio unhoods the Friar—to reveal the Duke.

In the middle of Act 3, at a dark moment, the plot turns. The Duke speaks of Mariana, abandoned by Angelo, now in the “moated grange.” Tennyson’s famous monologue “Mariana.” Pompey and Mistress Overdone are arrested. Lucio has gotten a prostitute pregnant and refuses marriage and child support.

When Isabella informs Claudio of Angelo’s offer, that his life may be saved if she has sex with Angelo, in terror of death he begs her to do it. Her cold, angry response, lacking all compassion, is absolutely unChristian, and we have to probe her deeper psychology, her need to be sheltered from life and its imperfections.

Angelo is reluctant to come right out and say it, but finally tells Isabella that she must give herself up to him sexually in order to save her brother’s life. The Duke, as Friar, counsels Claudio that he should be detached about death because life is not worth living. This is a possible religious attitude, though not one that Shakespeare’s comedies ever endorse.

Elbow, the Constable, has arrested Pompey because something insulting was said to his wife when she entered the whorehouse to ask for stewed prunes. Elbow is so confused that we never learn more. Isabella pleads for her brother’s life, and Angelo, after she leaves, discovers he is sexually obsessed with her.

The Duke of Vienna puts young Angelo in charge in his absence, but disguises himself as a Friar and intends to observe what goes on in his absence. Angelo has Claudio arrested because his fiancée Julietta is pregnant, though they are engaged in a binding, though secret contract. Lucio goes to the convent to fetch Claudio’s sister Isabella to plead to Angelo for Claudio’s life.

The common pattern of all three plots in Twelfth Night: a deadlocked conflict of opposites into which a third factor enters to transform the situation. In all three plots, this involves a character with two identities and gender ambiguity. Introduction to Measure for Measure: the meaning of the designation “problem play.”