Midway through his life, Dante wakes up in a dark, unfamiliar forest. He attempts to climb up a mountain, but his path is blocked by a leopard, a lion, and a wolf. The spirit of the Roman poet Virgil appears to him and tells him that he must take another path out of the forest. Dante's beloved Beatrice, who is now deceased and in heaven, has sent Virgil to guide Dante on a journey through hell, so that he can ascend through purgatory to heaven.
Dante and Virgil enter hell and first see a group of suffering neutral souls who committed to neither evil nor good. They next come to the river Acheron and see Charon, an old man who ferries souls across the river into hell. Charon first refuses to transport Dante, because he is a living soul, but Virgil tells him that Dante's journey is sanctioned by God, so Charon relents.
In the first circle of hell, Dante sees souls who did not sin, but died either unbaptised or before the time of Jesus. Here, he sees many virtuous pagans, including famous figures of classical Greek and Roman history, philosophy, and literature. Virgil introduces Dante to other famous poets of antiquity—Homer, Horace, Ovid, and Lucan—who welcome Dante into their esteemed literary company.
Virgil leads Dante on to the second circle of hell, which is darker and full of more suffering and screaming. Here they see Minos, the judge of the underworld, who dictates where in hell souls will be punished. Like Charon, he tries to stop Dante, since he is a living soul. Again, Virgil says that Dante's journey is divinely willed, and Minos lets him pass. Dante sees souls endlessly blown about by wind and storm, which he learns are the souls of those whose sin was lust. Dante points out several famous souls and Dante, moved with pity, asks if he can speak to a pair of souls. One of the souls, Francesca da Rimini, tells Dante her story. She had an affair with her husband's brother, Paolo Malatesta, and now the two of them are punished together here. Dante faints from pity at hearing Francesca's story.
When Dante awakens, he is in the third circle of hell, where Cerberus, a monstrous three-headed dog, mauls and bites sinners. Virgil throws handfuls of dirt into Cerberus' three mouths, subduing the creature so that he and Dante can walk past it. The soul of Ciacco (punished here for gluttony) recognizes Dante and speaks to him, foretelling political strife for Florence and begging Dante to speak of him back on earth.
At the entrance to the fourth circle of hell, Pluto stands in Dante and Virgil's way. Virgil shouts at Pluto, again saying that Dante's journey is willed by God, and Pluto falls to the ground. In the fourth circle, Dante sees spendthrifts and hoarders of money. In the marsh where the river Styx ends, Dante sees the wrathful, who are endlessly fighting each other madly.
Dante and Virgil come to a tower and are met by Phlegyas, who transports Dante and Virgil across the Styx. During the boat ride, Filippo Argenti grabs onto the boat and asks Dante what he, a living soul, is doing here. Virgil pushes Filippo back into the marshy waters. After crossing the Styx, Dante and Virgil come to the gate of Dis. A group of fallen angels shut the gate and refuse to let Virgil and Dante pass. The Furies appear and threaten to summon Medusa to turn Dante to stone. Virgil tells Dante to cover his eyes, but before Medusa appears an angel arrives. The angel rebukes the inhabitants of Dis trying to thwart Dante's journey and opens the gate by simply touching it with a wand. Dante and Virgil walk through the gate and see a field with burning tombs, within which heretics are punished. Dante speaks to one of these heretics, a fellow Florentine named Farinata. While talking to Farinata, Dante is interrupted by Cavalcante dei Cavalcanti, who asks about his son, one of Dante's friends. Farinata explains to Dante that souls in hell can see the future, but not the present. Dante and Virgil reach a cliff overlooking the lower parts of hell. Virgil suggests they take a break to get accustomed to the stench of lower hell and takes this opportunity to explain the layout of the rest of hell to Dante.
Virgil leads Dante down to the seventh circle of hell, where their path is blocked by the half-bull, half-man creature known as the minotaur. Virgil insults the creature, who thrashes around madly, letting Dante and Virgil sneak past. Virgil points out the Phlegethon, a river of boiling blood in which those who committed violence against others are punished. Centaurs roam the banks of the river, making sure no souls get out. The centaurs find Dante and Virgil, and Virgil convinces the centaur Nessus to allow Dante to ride him across a shallow part of the Phlegethon.
Virgil and Dante then enter a dark forest where the harpies dwell. When Dante plucks a branch from a tree, it bleeds and cries out in pain. The tree turns out to be the spirit of Pier delle Vigne, who committed suicide. Pier explains that the souls of suicides come to this forest and grow into trees. The harpies then eat their leaves, causing them great pain. Suddenly, two men run by, being chased by hounds. One jumps into a bush to hide, but is found and eaten by the hounds. Dante then speaks with the bush, which turns out to be the soul of a formerly living man. The bush has been hurt by the running man and, telling Dante that he was a man from Florence, begs Dante to gather its scattered leaves. Dante does so, before moving on.
Dante follows Virgil to a desert with burning sands, where fire falls from the sky. Dante sees numerous sinners walking around the desert or lying in the burning sands, including a giant man named Capaneus, who scorned God. Virgil and Dante come to a river whose banks are safe from the burning sands and falling fire. Before they proceed, Virgil explains the source of hell's rivers: the trickling stream of tears falling from a giant man underneath Crete. As Dante walks along the river, he finds Brunetto Latini, his old teacher, who predicts great fame for Dante and names several famous sinners around them. Latini asks Dante to remember his work, the Thesaurus, so that he may live on through it. After leaving Latini behind, Dante is stopped by three noble Florentines: Guido Guerra, Tegghiaio Aldobrandi, and Jacopo Rusticucci. They encourage Dante to seek fame, praise his speaking ability, and ask about the city of Florence. Dante and Virgil then come to where the river falls in a huge waterfall down to the eighth circle of hell. Virgil throws Dante's rope-belt over the waterfall and in response to the signal a huge monster flies up to where they are standing.
The winged monster is Geryon, whom Virgil talks to and gets to transport Dante and him down to the eighth circle. This circle of hell is divided into ten circular trenches surrounding a deep well. In the first trench, Dante recognizes Venedico Caccianemico, who admits to selling his sister away to a lustful nobleman, as well as the mythological hero Jason. In the second trench, Dante sees Alessio Interminei, a flatterer, and Virgil points out Thais, a courtesan who told her lovers that sex with them was a miracle. In the third trench, Dante sees Simonists, those who bought or sold sacred objects, church offices, or pardons. Among these is Pope Nicholas III, who angrily says that his successor to the papacy will soon him join him here. He also predicts that the next pope will be even more evil than the current one. The fourth trench holds sorcerers and seers. For attempting to see too far ahead, they now have their heads turned around, facing out over their backs, so that they can only see backwards (and must walk backwards, too). Dante weeps at this sight of bodily disfigurement, and Virgil criticizes him for crying at God's divine justice. Virgil points out Amphiaraus, Tiresias, and Manto, three famous seers from classical mythology.
In the fifth trench, a group of devils try to attack Virgil, but he speaks to them, telling them that he and Dante are on a journey ordained by God. The leader of this group of devils, Malacoda, sends a group of devils to guide Dante and Virgil to the next trench. While walking with Dante and Virgil, the devils hook a sinner up out of the pitch, who talks to Virgil and Dante, telling them he was from Navarre. He tells Dante that he will call forward seven Italians who are in the pitch, if he will get the devils to stop torturing him. While the devils argue about this possible deal, the sinner takes the opportunity to dive back into the pitch, evading the devils.
In the sixth trench, hypocrites walk around slowly, weighed down by gilded cloaks lined with heavy lead. Dante speaks with two friars here, who also point out Caiaphas, the man who came up with the idea to crucify Jesus and is now crucified on the ground. In the seventh trench, Dante sees serpents and lizards chasing after and stinging sinners. One man is struck by a snake and burns to ashes, but then the ashes immediately come together to form into the man again. This man identifies himself as Vanni Fucci, who robbed a church. Vanni curses God and runs off, with a snake curling around his throat. Dante sees four souls: three men and a six-legged worm. The worm clings to one of the men until they merge into one creature, which then slithers off. A lizard comes up and exchanges bodies with another of the men, and the third runs off to chase this lizard.
In the eighth trench, Dante sees many twinkling flames. Virgil tells him that under each flame is the soul of a sinner. Virgil shows Dante the twin flame of Ulysses and Diomedes and speaks to them for Dante. Ulysses tells them his story: after returning home from the Trojan War, he tried to sail to the ends of the earth, but God sent a whirlwind to wreck his ship and he drowned. Before Dante and Virgil leave this trench, they speak with Guido da Montefeltro, an Italian who is punished for giving the pope false counsel. The pope promised to absolve Guido's sins in advance of his committing them, but this did not work because Guido did not actually repent his sins, so he still ended up in hell. Dante sees sowers of discord in the ninth trench, who are literally split open by a devil wielding a sword. He talks with Mohammed and Pier da Medicina, who points out some other sinners. Dante sees Bertrand de Born, who is punished for convincing a king to kill his father by having his head cut off. He walks around holding his head in his hands. Dante looks around for his deceased relative Geri del Bello, but Virgil tells him Geri already passed by, looking angrily at Dante. Dante realizes that Geri is angry because no one in their family has avenged his violent death. Dante and Virgil continue on to the tenth trench.
The souls in the tenth trench are falsifiers and suffer from horrible diseases. Dante talks with two alchemists, Griffolino d'Arezzo and Capocchio. He sees two other souls running about rabid, which Griffolino identifies as Gianni Schicchi and Myrrha. Dante then talks with Adam, an Italian counterfeiter from Brescia who is grotesquely bloated and swollen. Adam points out two other sinners, Sinon and the wife of Potiphar, and then gets into a feud with Sinon. Dante is entertained by watching the two sinners fight, and Virgil scolds him for enjoying this vulgar entertainment.
Dante and Virgil continue their journey forward and Dante thinks he sees towers surrounding a well in the dark distance. As they get closer, though, Dante realizes they are giants, with the bottom halves of their bodies stuck into the ground. Virgil identifies some of the giants and then talks to Antaeus, a giant who is free to move around. Antaeus carries Virgil and Dante down the well that leads to the ninth circle of hell and deposits them there.
The lowest circle of hell is made up of the frozen lake Cocytus. Sinners are submerged in the ice, most with only their heads sticking out. Dante speaks to several souls before accidentally stepping on the head of Bocca degli Abati. Bocca refuses to tell Dante his name and Dante angrily grabs his hair, threatening to pull it out. Bocca still does not say his name, but another soul calls out to him, revealing his name. Dante recognizes Bocca as a traitor to Florence and tells him that his name will live on in infamy.
Dante sees two souls frozen together with one eating the other's head. He speaks to the one eating the other's head, who says that he is Count Ugolino from Pisa and he is devouring the head of Archbishop Ruggieri. Ruggieri imprisoned Ugolino and his children in a tower where they starved to death. Dante sees two other sinners—Friar Alberigo and Branca d'Oria—whose souls came to hell even before they died. Dante then sees Lucifer, whose humongous body towers out of the ice. He has three mouths, and each one holds a sinner in its teeth. The center mouth holds Judas, while the other two devour Brutus and Cassius. Dante holds onto Virgil as they climb up Lucifer's body and out of hell. They reach an outcropping of rock and walk into a cavern where the river Lethe begins as a small stream. They climb out of a hole, onto the island where Mt. Purgatory is located. Finally outside of hell, Dante looks up and can once more see the bright stars in the sky.