At the age of thirty-five, on the night of Good Friday in the year 1300, Dante finds himself lost in a dark wood and full of fear. He sees a sun-drenched mountain in the distance, and he tries to climb it, but three beasts, a leopard, a lion, and a she-wolf, stand in his way. Dante is forced to return to the forest where he meets the spirit of Virgil, who promises to lead him on a journey through Hell so that he may be able to enter Paradise. Dante agrees to the journey and follows Virgil through the gates of Hell.
The two poets enter the vestibule of Hell where the souls of the uncommitted are tormented by biting insects and damned to chase a blank banner around for eternity. The poets reach the banks of the river Acheron where souls await passage into Hell proper. The ferryman, Charon, reluctantly agrees to take the poets across the river to Limbo, the first circle of Hell, where Virgil permanently resides. In Limbo, the poets stop to speak with other great poets, Homer, Ovid, Horace, and Lucan, and then enter a great citadel where philosophers reside.
Dante and Virgil enter Hell proper, the second circle, where monster, Minos, sits in judgment of all of the damned, and sends them to the proper circle according to their sin. Here, Dante meets Paolo and Francesca, the two unfaithful lovers buffeted about in a windy storm.
The poets move on to the third circle, the Gluttons, who are guarded by the monster Cerberus. These sinners spend eternity wallowing in mud and mire, and here Dante recognizes a Florentine, Ciacco, who gives Dante the first of many negative prophesies about him and Florence.
Upon entering the fourth circle, Dante and Virgil encounter the Hoarders and the Wasters, who spend eternity rolling giant boulders at one another.
They move to the fifth circle, the marsh comprising the river Styx, where Dante is accosted by a Florentine, Filippo Argenti; he is amongst the Wrathful that fight and battle one another in the mire of the Styx.
The city of Dis begins Circle VI, the realm of the violent. The poets enter and find themselves in Circle VI, realm of the Heretics, who reside among the thousands in burning tombs. Dante stops to speak with two sinners, Farinata degli Uberti, Dante's Ghibelline enemy, and Cavalcante dei Cavalcanti, father of Dante's poet friend, Guido.
The poets then begin descending through a deep valley. Here, they meet the Minotaur and see a river of boiling blood, the Phlegethon, where those violent against their neighbors, tyrants, and war-makers reside, each in a depth according to their sin.
Virgil arranges for the Centaur, Nessus, to take them across the river into the second round of circle seven, the Suicides. Here Dante speaks with the soul of Pier delle Vigne and learns his sad tale.
In the third round of Circle VII, a desert wasteland awash in a rain of burning snowflakes, Dante recognizes and speaks with Capaneus, a famous blasphemer. He also speaks to his beloved advisor and scholar, Brunetto Latini. This is the round held for the Blasphemers, Sodomites, and the Usurers.
The poets then enter Circle VIII, which contains ten chasms, or ditches. The first chasm houses the Panderers and the Seducers who spend eternity lashed by whips. The second chasm houses the Flatterers, who reside in a channel of excrement. The third chasm houses the Simonists, who are plunged upside-down in baptismal fonts with the soles of their feet on fire. Dante speaks with Pope Nicholas, who mistakes him for Pope Boniface. In the fourth chasm, Dante sees the Fortune Tellers and Diviners, who spend eternity with their heads on backwards and their eyes clouded by tears.
At the fifth chasm, the poets see the sinners of Graft plunged deeply into a river of boiling pitch and slashed at by demons.
At the sixth chasm, the poets encounter the Hypocrites, mainly religious men damned to walk endlessly in a circle wearing glittering leaden robes. The chief sinner here, Caiaphas, is crucified on the ground, and all of the other sinners must step on him to pass.
Two Jovial friars tell the poets the way to the seventh ditch, where the Thieves have their hands cut off and spend eternity among vipers that transform them into serpents by biting them. They, in turn, must bite another sinner to take back a human form.
At the eighth chasm Dante sees many flames that conceal the souls of the Evil Counselors. Dante speaks to Ulysses, who gives him an account of his death.
At the ninth chasm, the poets see a mass of horribly mutilated bodies. They were the sowers of discord, such as Mahomet. They are walking in a circle. By the time they come around the circle, their wounds knit, only to be opened again and again. They arrive at the tenth chasm the Falsifiers. Here they see the sinners afflicted with terrible plagues, some unable to move, some picking scabs off of one another.
They arrive at the ninth circle. It is comprised of a giant frozen lake, Cocytus, in which the sinners are stuck. Dante believes that he sees towers in the distance, which turn out to be the Giants. One of the Giants, Antaeus, takes the poets on his palm and gently places them at the bottom of the well.
Circle IX is composed of four rounds, each housing sinners, according to the severity of their sin. In the first round, Caina, the sinners are frozen up to their necks in ice.
In the second round, Antenora, the sinners are frozen closer to their heads. Here, Dante accidentally kicks a traitor in the head, and when the traitor will not tell him his name, Dante treats him savagely. Dante hears the terrible story of Count Ugolino, who is gnawing the head and neck of Archbishop Ruggieri, due to Ruggieri's treacherous treatment of him in the upper world.
In the third round, Ptolomea, where the Traitors to Guests reside, Dante speaks with a soul who begs him to take the ice visors, formed from tears, out of his eyes. Dante promises to do so, but after hearing his story refuses.
The fourth round of Circle IX, and the very final pit of Hell, Judecca, houses the Traitors to Their Masters, who are completely covered and fixed in the ice, and Satan, who is fixed waist deep in the ice and has three heads, each of which is chewing a traitor: Judas, Brutus, and Cassius.
The poets climb Satan's side, passing the center of gravity, and find themselves at the edge of the river Lethe, ready to make the long journey to the upper world. They enter the upper world just before dawn on Easter Sunday, and they see the stars overhead.