For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Ante-Purgatory: Dante and Virgil arrive on the shores of Purgatory. They meet Cato; at his command, Dante is outfitted with a new rush belt. As he makes his way through the four spurs of ante-Purgatory, Dante meets and speaks to such figures as Manfred, Belacqua, Buonconte da Montefeltro, Sordello, Nino Visconti, and a bunch of 13th Century kings.
He rants against Italy’s political corruption and sees angels driving off a serpent in the Valley of the Rulers. He dreams of an eagle. At the gate of Purgatory, Dante walks the three steps representing the Sacrament of Penance and has seven Ps inscribed on his forehead by the guardian angel.
Act II
Purgatory Proper: Dante and Virgil traverse the seven terraces of Purgatory, meeting groups of punished penitents, seeing and hearing examples of punished vice as well as counterexamples of corresponding virtues. At the end of each terrace, an angel removes a P from Dante’s forehead and welcomes him onto the new terrace.
Significant events include Dante’s taking-on of the position of the Prideful; his discussion with Marco Lombardo about free will; Virgil’s discourse on love; Dante’s dream of the Siren; the meeting with Statius and the story of his conversion; the conversation with the poets Forese Donati, Bonagiunta da Lucca, and Guinizzelli; Statius’ explanation of the aery body of souls; the passage through fire; and Dante’s dream about Leah and Rachel.
Act III
Earthly Paradise: Dante meets Matilda, who explains the origin of the Earthly Paradise to him. At the banks of the river Lethe, Dante sees an extraordinary procession. At the end of it, he meets Beatrice. Virgil disappears, much to Dante’s distress. Beatrice accuses Dante of his sins. Dante is shamed and confesses, then swoons.
While he’s unconscious, Matilda immerses him in the Lethe. After he wakes up, Beatrice goes into long and complex prophecies about the Church. They come to the Tree of Divine Justice. Beatrice charges Dante with the task of writing about his experiences here with truth. The chariot transforms into a monster, then a whore who sleeps with a giant. Beatrice prophecies God’s vengeance against the whore and her giant. Matilda immerses Dante in the river Eunoe, and Dante is readied for ascent into Paradise.