The narrative follows Dante and Virgil as they arrive at the shores of Purgatory, a mountain rising steeply from the ocean in the southern hemisphere. After being cleansed and girded with a rush of humility by Cato, the guardian of the realm, the poets witness the arrival of souls delivered by an angelic pilot.
As they ascend through the various terraces, they encounter souls undergoing penance for the seven deadly sins: pride, envy, anger, sloth, avarice, gluttony, and lust. Each terrace presents unique trials, such as the proud carrying crushing weights and the envious having their eyes sewn shut with wire. Along the way, Dante engages in profound theological and philosophical discussions with historical figures and poets, including Casella, Sordello, Manfredi, and the Roman poet Statius, who eventually joins them.
Throughout the journey, Virgil serves as a wise mentor and guide, explaining the nature of love, free will, and moral order. However, as they reach the summit of the mountain and enter the Terrestrial Paradise, Virgil's guidance comes to an end because unbaptized souls cannot enter Heaven.
In the Garden of Eden, Dante is met by Matilda, who guides him through the symbolic rivers of Lethe, which erases the memory of sin, and Eunoe, which restores the memory of good deeds. Here, Beatrice appears on a triumphal chariot to replace Virgil as Dante's ultimate guide. She subjects him to a severe examination of conscience, leading him to confess his past transgressions and repent.
The poem concludes with a grand allegorical pageant depicting the history and corruption of the Church, culminating in Dante's spiritual rebirth. Having been completely purified and made ready to ascend to the stars, the pilgrim stands at the threshold of eternal grace.