Dante is lost in a dark wood at the midpoint of his life. Three beasts block his ascent. Virgil appears as his guide, sent by Beatrice. They pass through the Gate of Hell, traverse the vestibule of the uncommitted, cross the river Acheron, and enter Limbo where virtuous pagans dwell. In the Second Circle, the lustful are blown by eternal winds. Dante speaks with Francesca da Rimini and faints from pity.

Dante descends through the circles of gluttony, avarice, and wrath. The wrathful fight in the Styx while the sullen lie submerged. At the walls of the City of Dis, fallen angels refuse entry until a divine messenger forces the gates open. Inside, heretics burn in open tombs. Virgil explains the moral structure of Hell: incontinence above, violence and fraud below.

Guarded by the Minotaur, the Seventh Circle punishes violence in three concentric rings: violence against others (a river of boiling blood), violence against the self (suicides transformed into trees), and violence against God, nature, and art (a burning desert with rain of fire). Dante meets centaurs, encounters the suicide-trees, and speaks with his former mentor Brunetto Latini among the sodomites.

Riding the monster Geryon into the Eighth Circle, Dante enters Malebolge ('Evil Ditches') — ten concentric trenches punishing fraud. Seducers are whipped, flatterers swim in excrement, simonists are planted headfirst in holes with feet on fire, soothsayers have heads twisted backward, barrators boil in pitch, hypocrites wear leaden cloaks, and thieves undergo grotesque serpentine metamorphoses.

In the eighth ditch, evil counselors burn inside tongues of flame. Ulysses tells the story of his final, fatal voyage beyond the Pillars of Hercules. Guido da Montefeltro recounts how a pope's false promise damned him. In the ninth and tenth ditches, sowers of discord are hacked apart by a demon's sword, and falsifiers suffer diseases that mirror their corruptions.

Giants stand around the rim of the lowest pit. Dante and Virgil are lowered into the Ninth Circle, where traitors are frozen in the ice lake Cocytus. Four zones punish traitors to kindred, country, guests, and benefactors with increasing severity. Count Ugolino gnaws eternally on Archbishop Ruggieri's skull. At the center, Satan — a three-faced, weeping, frozen giant — chews Judas, Brutus, and Cassius in his three mouths. Dante and Virgil climb down Satan's body and emerge to see the stars.