Inferno opens on the evening of Good Friday in the year 1300. Traveling through a dark wood, Dante Alighieri has lost his path and now wanders fearfully through the forest. The sun shines down on a mountain above him, and he attempts to climb up to it but finds his way blocked by three beasts—a leopard, a lion, and a she-wolf. Frightened and helpless, Dante returns to the dark wood. Here he encounters the ghost of Virgil, the great Roman poet, who has come to guide Dante back to his path, to the top of the mountain. Virgil says that their path will take them through Hell and that they will eventually reach Heaven, where Dante’s beloved Beatrice awaits. He adds that it was Beatrice, along with two other holy women, who, seeing Dante lost in the wood, sent Virgil to guide him.

Virgil leads Dante through the gates of Hell, marked by the haunting inscription “abandon all hope, you who enter here” (III.7). They enter the outlying region of Hell, the Ante-Inferno, where the souls who in life could not commit to either good or evil now must run in a futile chase after a blank banner, day after day, while hornets bite them and worms lap their blood. Dante witnesses their suffering with repugnance and pity. The ferryman Charon then takes him and his guide across the river Acheron, the real border of Hell. The First Circle of Hell, Limbo, houses pagans, including Virgil and many of the other great writers and poets of antiquity, who died without knowing of Christ. After meeting Horace, Ovid, and Lucan,

Dante continues into the Second Circle of Hell, reserved for the sin of Lust. At the border of the Second Circle, the monster Minos lurks, assigning condemned souls to their punishments. He curls his tail around himself a certain number of times, indicating the number of the circle to which the soul must go. Inside the Second Circle, Dante watches as the souls of the Lustful swirl about in a terrible storm; Dante meets Francesca, who tells him the story of her doomed love affair with Paolo da Rimini, her husband’s brother; the relationship has landed both in Hell.

In the Third Circle of Hell, the Gluttonous must lie in mud and endure a rain of filth and excrement. In the Fourth Circle, the Avaricious and the Prodigal are made to charge at one another with giant boulders. The Fifth Circle of Hell contains the river Styx, a swampy, fetid cesspool in which the Wrathful spend eternity struggling with one another; the Sullen lie bound beneath the Styx’s waters, choking on the mud. Dante glimpses Filippo Argenti, a former political enemy of his, and watches in delight as other souls tear the man to pieces.

Virgil and Dante next proceed to the walls of the city of Dis, a city contained within the larger region of Hell. The demons who guard the gates refuse to open them for Virgil, and an angelic messenger arrives from Heaven to force the gates open before Dante. The Sixth Circle of Hell houses the Heretics, and there Dante encounters a rival political leader named Farinata. A deep valley leads into the First Ring of the Seventh Circle of Hell, where those who were violent toward others spend eternity in a river of boiling blood.

Virgil and Dante meet a group of Centaurs, creatures who are half man, half horse. One of them, Nessus, takes them into the Second Ring of the Seventh Circle of Hell, where they encounter those who were violent toward themselves (the Suicides). These souls must endure eternity in the form of trees. Dante there speaks with Pier della Vigna. Going deeper into the Seventh Circle of Hell, the travelers find those who were violent toward God (the Blasphemers); Dante meets his old patron, Brunetto Latini, walking among the souls of those who were violent toward Nature (the Sodomites) on a desert of burning sand. They also encounter the Usurers, those who were violent toward Art.

The monster Geryon transports Virgil and Dante across a great abyss to the Eighth Circle of Hell, known as Malebolge, or “evil pockets” (or “pouches”); the term refers to the circle’s division into various pockets separated by great folds of earth. In the First Pouch, the Panderers and the Seducers receive lashings from whips; in the second, the Flatterers must lie in a river of human feces. The Simoniacs in the Third Pouch hang upside down in baptismal fonts while their feet burn with fire. In the Fourth Pouch are the Astrologists or Diviners, forced to walk with their heads on backward, a sight that moves Dante to great pity.

In the Fifth Pouch, the Barrators (those who accepted bribes) steep in pitch while demons tear them apart. The Hypocrites in the Sixth Pouch must forever walk in circles, wearing heavy robes made of lead. Caiphas, the priest who confirmed Jesus’ death sentence, lies crucified on the ground; the other sinners tread on him as they walk. In the horrifying Seventh Pouch, the Thieves sit trapped in a pit of vipers, becoming vipers themselves when bitten; to regain their form, they must bite another thief in turn.

In the Eighth Pouch of the Eighth Circle of Hell, Dante speaks to Ulysses, the great hero of Homer’s epics, now doomed to an eternity among those guilty of Spiritual Theft (the False Counselors) for his role in executing the ruse of the Trojan Horse. In the Ninth Pouch, the souls of Sowers of Scandal and Schism walk in a circle, constantly afflicted by wounds that open and close repeatedly. In the Tenth Pouch, the Falsifiers suffer from horrible plagues and diseases.

Virgil and Dante proceed to the Ninth Circle of Hell through the Giants’ Well, which leads to a massive drop to Cocytus, a great frozen lake. The giant Antaeus picks Virgil and Dante up and sets them down at the bottom of the well, in the lowest region of Hell. In Caina, the First Ring of the Ninth Circle of Hell, those who betrayed their kin stand frozen up to their necks in the lake’s ice.

In Antenora, the Second Ring, those who betrayed their country and party stand frozen up to their heads; here Dante meets Count Ugolino, who spends eternity gnawing on the head of the man who imprisoned him in life. In Ptolomea, the Third Ring, those who betrayed their guests spend eternity lying on their backs in the frozen lake, their tears making blocks of ice over their eyes. Dante next follows Virgil into Judecca, the Fourth Ring of the Ninth Circle of Hell and the lowest depth. Here, those who betrayed their benefactors spend eternity in complete icy submersion.

A huge, mist-shrouded form lurks ahead, and Dante approaches it. It is the three-headed giant Lucifer, plunged waist-deep into the ice. His body pierces the center of the Earth, where he fell when God hurled him down from Heaven. Each of Lucifer’s mouths chews one of history’s three greatest sinners: Judas, the betrayer of Christ, and Cassius and Brutus, the betrayers of Julius Caesar. Virgil leads Dante on a climb down Lucifer’s massive form, holding on to his frozen tufts of hair. Eventually, the poets reach the Lethe, the river of forgetfulness, and travel from there out of Hell and back onto Earth. They emerge from Hell on Easter morning, just before sunrise.

Purgatorio picks up right where Inferno left off—Dante and Virgil have just emerged from their tour through Hell. (Not going to lie: Dante's trilogy of wacky afterworld adventures is a bit like the Hangover trilogy... the first one is definitely the most surprising and shocking. But don't worry, the second and third are pretty fascinating as well.)

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. Fun times!

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 ( the letter “P” is carved seven times into Dante's forehead, representing seven instances of “peccatum” or sin) 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.

Dante and his beloved, Beatrice, begin their journey a few days after Easter Sunday. From the Earthly Paradise at Purgatory’s summit, the two are lifted skyward by a kind of heavenly gravity. Dante finds that he can withstand brief glances at the blazing sun (the lights of Heaven representing God), but usually he must resort to gazing at the eyes of Beatrice (who represents indirect revelation of God). However, even that is sometimes too much for his vision to handle.

Beatrice and Dante first visit the heavenly sphere of the Moon, the first of nine spheres. Observing the varied markings on the Moon’s surface, Dante and Beatrice discuss God’s providence—the way his will is expressed in widely varying ways throughout creation. Dante also speaks with souls residing in the Moon’s sphere, including Piccarda, who dwells in this cloudy, variable sphere because of the inconstancy of her will during life. However, Piccarda is perfectly happy with her destiny because her will is completely in harmony with God’s, and she cannot desire anything besides what God gives.