The Inferno follows the wanderings of the poet Dante as he strays off the rightful and straight path of moral truth and gets lost in a dark wood. Just as three wild animals threaten to attack him, Dante is rescued by the ghost of Virgil, a celebrated Roman poet and also Dante’s idol. When asked why in hell (pun intended) he came, Virgil answers that the head honchos of Heaven – the Virgin Mary and Santa Lucia – felt sorry for Dante and asked the deceased love-of-Dante’s-life, Beatrice, to send someone down to help him. And voila! Virgil to the rescue! He’s an appropriate guide because he’s very much like Dante, a fellow writer and famous poet.
For the rest of the Inferno, Virgil takes Dante on a guided tour of Hell, through all its nine circles and back up into the air of the mortal world. The first circle of Hell (Limbo), considered pre-Hell, just contains all of the unbaptized and good people born and before the coming of Christ, who obviously couldn’t be saved by him. Virgil resides here, along with a bunch of other Greek and Roman poets. In the second circle, lustful sinners are tossed around by endless storms. Dante speaks to the soul of Francesca da Rimini, a woman who was stuck in a loveless, arranged marriage and committed adultery when she fell in love with a dashing youth named Paolo.
Dante then awakes in the third circle, where the Gluttonous sinners suffer under a cold and filthy rain. Dante talks to the glutton Ciacco, a famous Florentine, who prophesies disaster for Florence. Virgil leads Dante on to the fourth circle, where the Avaricious (greedy people) and Prodigal (reckless spenders) roll heavy weights in endless circles. The next stop on the tour is the fifth circle, where the Wrathful and Sullen are immersed in the muddy river Styx. While they are crossing the Styx, a sinner named Filippo Argenti reaches out to Dante (presumably for help), but Dante angrily rejects him.
Now at the gates of a city called Dis, Virgil takes it upon himself to persuade the demon guards to let them pass. Unexpectedly, he fails. This means that instead of continuing on with the journey, Dante and Virgil must wait for an angel to come down and force open the gates for them. After passing the city of Dis, our dynamic duo enters the sixth circle, where the Heretics lay in fiery tombs. Dante talks to Farinata degli Uberti, who predicts that Dante will have difficulty returning to Florence from exile.
As they cross from the sixth to the seventh circle, where the Violent are punished, Virgil finally begins explaining the layout of Hell. We soon learn that all human sins are divided into three big categories: incontinence (or lacking self-control), violence, and fraud. Everything Dante has witnessed so far has fallen under the first category. The seventh circle will show all the violent sinners. Then the final two circles will include all the sinners of ordinary fraud and treacherous fraud.
Finally, Dante and Virgil ready themselves to cross to the eighth circle. Dante, at Virgil’s command, summons the beast Geryon from the depths with a cord wrapped around his waist. Virgil stays to talk with the beast while urging Dante to look at the last of the Violent sinners. When Dante comes back, they mount Geryon and ride the beast during the descent into the eighth circle.
The eighth circle contains ten pouches, each containing different types of sinners. When Dante and Virgil reach the third pouch where simonists (people who use money to get high positions in the Church) are buried headfirst in the ground while their feet roast in flames, Dante works up the courage to speak to one of the sinners. The soul of Pope Nicholas III mistakes Dante (understandably, because he can’t see him) for his successor and Dante’s hated enemy, Pope Boniface VIII, come to replace him in punishment.
As Dante and Virgil traverse the fifth pouch, in which barrators (or corrupt politicians) are forked by demons and plunged into a river of boiling pitch, Virgil bravely approaches the ruthless demons and demands safe passage across the river. When the sinister demons see that he is sent by God, the head demon, Malacoda, tells Virgil that the nearest bridge has been broken and so assigns ten demons to escort him to the next bridge.
Afraid of the demons, Dante and Virgil escape by crossing into the sixth pouch, where the demons cannot follow. Here, they run into the hypocrites who are forced to stand clothed in robes of lead. After talking to a few of them, Virgil asks for directions to the next pouch. In the valley of the sixth pouch, thieves are continually bitten by serpents whose venom burns them into ashes. Dante converses with one of these sinners, Vanni Fucci, and discovers that he is being punished for stealing sacred relics from the Church. After spiting Dante and committing blasphemy, Fucci is dragged away by serpents.
Our heroes hurry into the eighth pouch, where fraudulent counselors are encased in flames. Ulysses, sharing one tongue of flame with Diomedes, tells his sinful tale to Dante: once home after his long voyage (recounted in the Odyssey), Ulysses was not content to fulfill his duties to his family and country. He longed for adventure so he gathered up his aging crew and set sail again, surpassing the boundaries of human exploration until, in the shadow of the Mount of Purgatory, he and his crew perished in a violent whirlpool.
In the ninth pouch, Dante witnesses the sowers of scandal and schism being disemboweled by a demon with a sword, healed, and punished again – eternally. Dante is so freaked out by this sight that he has to cover his ears to avoid hearing the moans as they pass into the tenth and last pouch.
In the tenth pouch, four different kinds of falsifiers are punished. As they leave, Virgil points out the sinning giants who are immobilized around them in punishment. Nimrod – who was responsible for building the Tower of Babel – has lost the ability to speak coherently. His words are gibberish. Virgil requests that one of the unbound giants, Antaneus, transport them in the palm of his hand down to the last circle of Hell. He complies.
The ninth circle of Hell, where traitors are punished, contains four different zones. The first one, called Caina (after Cain), features traitors to their kin immersed in ice up to their necks. In the second zone, Antenora, where traitors to their homeland suffer the same punishment, Dante is provoked by Bocca degli Abati and uncharacteristically threatens him with violence. He moves on to the third zone called Ptolomea, where traitors against their guests suffer, immobilized in ice and their tears frozen against their eyes. Dante promises to break the ice off of the eyes of one of them if he tells him his story. This sinner, Fra Alberigo, agrees and Dante learns that this level of sin is so evil that the sinner's soul is condemned to Hell even before his body dies on earth.
In the fourth the final zone, Judecca, where traitors against their benefactors are punished, Dante witnesses the king of Hell, the three-headed Lucifer, giant and frozen at the core. In his three mouths, Lucifer mechanically chews on the most evil mortal sinners – Judas, Brutus, and Cassius.
Now that they've finished their tour, Virgil tell Dante that it's time to leave Hell for good. With Dante clinging to Virgil’s back, the two climb down Lucifer’s massive body, which spans the diameter of the entire Earth, and arrive in the southern hemisphere. Here, Virgil and Dante follow a path back up to the surface of the Earth and emerge to see Heaven’s stars.