Purgatorio picks up right where Inferno left off – Dante and Virgil have just emerged from their tour through Hell. The two travelers find themselves on the island of Mount Purgatory at the dawn of a new day. On the shores of the island, Dante and Virgil watch a boat arrive. Guided by an angel, the boat shuttles a new batch of penitent souls to Purgatory. Like these souls, Dante is about to climb Mount Purgatory, learning lessons, and cleansing himself of sin in preparation for ascending to Heaven. Before beginning to scale the mountain, Dante and Virgil must first pass through ante-Purgatory. They meet a variety of souls, most of whom are shocked to see that Dante casts a shadow, showing that he's alive. Along their travels they pass though the First Spur of the Indolent and the Second Spur of the Late-Repentants. They travel to the Valley of the Rulers and meet a bunch of deceased kings. In the valley, a serpent appears at dusk, only to be driven away by two angels. The penitent souls are unable to travel in Purgatory at night, so, although Virgil is in a hurry, he and Dante rest until morning. Dante sleeps and dreams about an eagle abducting him. When he wakes up, he finds himself at the entrance to Purgatory proper. Virgil informs him that St. Lucia came while he slept and carried him to the gate to Purgatory. They climb the three steps to the gate, and the angel guarding the entrance carves seven P’s into Dante’s forehead.
Now in Purgatory proper, Dante and Virgil have seven terraces to pass through, each of which corresponds to one of the seven deadly sins. On the first terrace of the Prideful, Dante and Virgil observe in the wall of the cliff sculptures representing humility. They come across the Prideful penitents, who are being punished for their sin of pride by carrying massive weights on their backs. The penitents are permanently hunched over, and Dante takes on their bent position in order to speak with them. Dante remains in this position through the entire first terrace, identifying with the Prideful, until they reach the exit, where an angel erases one P from Dante’s forehead. Dante and Virgil climb to the second terrace of the Envious. Voices there call out examples of fraternal love. They witness the Envious penitents being punished by having their eyelids sewn shut with iron wire. Voices call out examples of punished envy. Dante and Virgil exit the second terrace, and another angel removes a P from Dante's forehead.
Now in the third terrace of the Wrathful, Dante has a vision containing examples of gentleness. Black smoke, the punishment of the Wrathful, envelops them, rendering them blind. In the smoke, they meet a man named Marco Lombardo, who discourses on free will and political corruption. Dante and Virgil meet the angel who removes the third P from Dante’s forehead.
As they travel to the fourth terrace of the Slothful, Virgil explains how love determines the structure of Purgatory. He continues to lecture on love and free will. The Slothful penitents, meanwhile, shout examples of zeal and show that their punishment is to run without rest. Dante has a nightmare about a Siren, but the next morning, they exit the terrace and an angel removes Dante’s fourth P.
Dante and Virgil ascend to the fifth terrace of the Avaricious and Prodigal, where they witness the penitents' punishment: lying stretched face down on the ground and bound by hand and foot. The penitents shout examples of poverty and generosity.
Suddenly, Mount Purgatory trembles. We learn that this happens every time a penitent soul becomes completely purged and ready to ascend to Heaven. An epic poet named Statius joins Dante and Virgil. He turns out to be a big fan of Virgil; and he is also the purged soul for whom the mountain trembled. The trio meets an angel who erases Dante’s fifth P.
On the sixth terrace of the Gluttonous, they encounter a strange tree. A disembodied voice cites examples of temperance. They encounter a man named Forese Donati, who explains the punishment of the Gluttonous as agonizing thirst and hunger. He points out the poet Bonagiunta da Lucca, who chats with Dante about poetry. At the exit of the sixth terrace, an angel removes Dante’s sixth P.
Dante, Virgil, and Statius climb to the seventh terrace of the Lustful. Reflecting on the thin penitents he encountered in the terrace of the Gluttonous, Dante asks how souls can grow lean if they don’t need food. Virgil cedes the floor to Statius, who explains the generation of the soul and their aerial bodies. Here among the Lustful, however, they witness the punishment of the penitents, who walk in flames. The Lustful shout examples of chastity. Dante meets the poet Guido Guinizzelli, whom he reveres, and also the poet Arnaut Daniel. At sunset, the travelers reach the exit to the seventh terrace, and an angel removes Dante’s final P. However, to leave the terrace, Dante must first walk through a wall of flames. He hesitates with fear, but Virgil lures him through with the promise that he will see Beatrice on the other side. Past the fire, Dante sleeps. In the morning, Virgil announces Dante’s readiness for the Earthly Paradise.
In the Earthly Paradise, Dante meets a woman named Matilda, who explains the origins of wind and water in the forest of the Earthy Paradise. At the banks of the river Lethe, an extraordinary procession passes by, halting before Dante. Virgil disappears, to Dante’s distress, but Beatrice appears. Beatrice, however, rebukes Dante for crying over Virgil’s disappearance. She continues accusing him of his sins and faults. Dante confesses to his sins, then passes out from the sight of Beatrice’s beauty. Matilda immerses the unconscious Dante in the waters of the Lethe and he wakes up. The procession proceeds to the Tree of Knowledge, where Dante falls asleep. When he wakes, Beatrice charges him with a mission: to observe and write down everything he sees here for use in his poetry when he goes back to earth. Dante witnesses the procession's chariot attacked by an eagle, a fox, the eagle again, and a dragon. Then the chariot turns into a whore, courted by a giant. Beatrice prophesies God’s vengeance on the dragon, whore, and giant. At the closing of Purgatorio, Matilda leads Dante to the river Eunoe, and immerses him in the water. He is now ready to ascend to Heaven, with Statius and Beatrice as his guides.