This is an outline of Inferno’s plot. For an outline of the structural organization of Dante’s hell as depicted in the Inferno, see here.
Canto I: Dante the Pilgrim is lost in a dark wood and prevented from leaving it by a leopard, a lion, and a she-wolf. Virgil appears and promises to lead him through hell and purgatory to paradise.
Canto II: Virgil explains to the hesitant Pilgrim that he had been sent by Beatrice, who had been sent by the Lady Lucia, who was in turn sent by the Virgin Mary on Dante’s behalf. Dante agrees to follow Virgil.
Canto III: Dante reads the inscription on the Gates of Hell and sees the souls of the Undecided suffering in the Vestibule. Virgil and Dante cross the Acheron in Charon’s boat.
Canto IV: Dante and Virgil enter Limbo, where the virtuous pagans live without pain or hope, and in their eternally unfulfilled desire to know God. They meet the other pagan poets (Homer, Horace, etc.) and many other historical and mythological figures.
Canto V: Passing Minos the judge of hell, the poets enter the circle of the lustful, where they see people who committed sins of passion whirled along by “battling winds” (V, 49). Dante talks to Francesca.
Canto VI: The poets pass Cerberus, who devours the fistful of mud thrown at it by Virgil. They meet the Gluttons. Dante talks with Ciacco and asks Virgil questions about the Last Judgment.
Canto VII: Passing Plutus, the god of wealth, the poets find the Prodigal and the Miserly rolling stones against each other. Dante questions Virgil about the nature of Fortune.
Canto VIII: While they are passing the sixth circle (the river Styx) in the boat of Phlegyas, Filippo Argenti, a Wrathful sinner, rises from the river. (The slothful are beneath the surface). Once across, Virgil speaks apart with the devils. They refuse to open the gates of the city of Dis, but Virgil assures Dante that someone is coming from Heaven to open the gates for them.
Canto IX: No one arrives. Virgil comforts Dante by telling him that he knows the way well. The Erinyes appear on the top of the tower and call for Medusa. An angel arrives, however, and opens the gates of the city, to reveal burning sarcophagi containing the heretics.
Canto X: Dante talks with the proud Farinata. While talking, Cavalcanti rises up and mistakenly assumes that his son Guido is dead. Dante asks Farinata to inform him that Guido is still alive, then leaves with Virgil.
Canto XI: Walking on, the poets find a stinking abyss, in which Pope Anastasius II is enclosed in a tomb. Virgil informs Dante about the organization of hell.
Canto XII: Leaving the heretics, the poets meet with the Minotaur, consumed in his own rage. He guards the sin of Violence. The first circle is the river of boiling blood, Phlegethon. Centaurs move along its bank and shoot down any sinner who shows his head above the surface. The poets are guided by Nessus across the river.
Canto XIII: The poets enter a wood guarded by Harpies. Instructed by Virgil, Dante breaks off a twig and finds that the plants are all suicides. Dante talks with Pier delle Vigne and witnesses a bush (a Florentine suicide) injured by sinners from the next ring.
Canto XIV: The poets see the Blasphemers, Userers, and Sodomites, all punished on the burning sand. Virgil accuses Capaneus and tells Dante about the Old Man of Crete, whose tears are the source of all the rivers in hell.
Canto XV: Walking along, Dante is accosted by his former teacher Brunetto Latini, a sodomite. Brunetto makes a prophecy regarding Florence and Dante’s future.
Canto XVI: Dante hears the sound of a distant waterfall. He converses with Jacopo Rusticucci, a sodomite in a revolving group of three. Virgil takes the cord around Dante’s waist and throws it down the Great Barrier, summoning Geryon.
Canto XVII: Geryon flies up from below. As Virgil negotiates with him, Dante sees three usurers, faceless and identified only from their money pouches. Virgil and Dante mount Geryon.
Canto XVIII: Geryon deposits Virgil and Dante on the edge of the first bolgia of the eighth circle. They see two rows of people walking in opposite directions and whipped by devils. Dante sees Venedico Caccianemico and Virgil points out the seducer Jason.
Canto XIX: The poets see simonists with their heads down in holes and legs and feet up in the air, the soles of which are burned by flame. A particularly twitchy pair of legs belongs to Pope Nicholas III, who mistakes Dante for Boniface VIII. Dante and the Pope have a highly rhetorical conversation. Virgil is pleased with Dante and carries him to the top of the next bolgia.
Canto XX: Dante sees the soothsayers of the Fourth bolgia, who walk backward crying, their heads twisted. Virgil points out several figures and tells Dante the true origin of his native town Mantua, named after Manto.
Canto XXI: On the bridge over the fifth bolgia, Dante and Virgil see devils thrusting sinners into the boiling pitch below. The guardians of this bolgia, the Malebranche devils, are obscene creatures. Their leader lies to Virgil about the bridges over the sixth bolgia, all of which had been broken when Christ descended into hell. Several devils escort the poets across the bolgia.
Canto XXII: Seeing the devils approach, a group of barrators all dive below the pitch, but a Navarrese who didn’t act fast enough is caught and tortured. Between his tortures, he tells Dante and Virgil his story. He then tricks the devils by promising them that if they stand back, he will summon more of his companions for their sport. When they do so, however, he dives beneath the pitch. The furious devils pick a fight with Alichino, the devil who suggested that they believe in the Navarrese in the first place, and in the fight, two devils drop into the pitch.
Canto XXIII: Sensing that the Malebranche devils may now come after them, Dante and Virgil quickly slid into the sixth Bolgia. There they see the hypocrites marching in single file, each one wearing a golden coat lined with lead inside. Two Jovial Friars tell Virgil that all the bridges over the Sixth Bolgia are broken, and Virgil realizes that he had been lied to by the Malebranche devil.
Canto XXIV: Virgil and Dante struggle up a landslide to the top of the seventh Bolgia. They come to the edge of the bank and see a man attacked by the snake. The man, Vanni Fucci, turns into ashes before becoming a man again.
Canto XXV: Three sinners come running. One of them is concerned with the disappearance of Cianfa. Cianfa has in fact become a snake and attacks Agnèl, with whom he merges into a hideous monster. Francesco Cavalcanti (Guercio) attacks Buoso and exchanges shapes with him, the former becoming a man and the latter becoming a snake. Puccio Sciancato is left unchanged.
Canto XXVI: Among the deceivers of the eighth bolgia, the poets see Ulysses and Diomedes enclosed in one flame. Virgil talks with Ulysses, who tells them the story of his last journey, in which he passed the pillars of Hercules and was drowned.
Canto XXVII: Guido da Montefeltro, another deceiver, asks Dante to tell him about events in the region of Italy where he came from. Then Guido speaks of himself and how he had tried to sin and repent at the same time.
Canto XXVIII: In the ninth Bolgia, Dante is horrified by the sight of mutilated bodies. Mahomet is split from chin to crotch, Ali is cleft from chin to crown, Pier da Medicina has his throat slit, his nose and one ear missing, Curio’s tongue is cut out, Mosca’s hands are cut off, and Bertran carries his own head as the perfect contrapasso.
Canto XXIX: Virgil rebukes Dante for showing inordinate interest in the sinners, but Dante says he is looking for a family member, Geri del Bello. As they walk to the tenth bolgia, they see Griffolino da Arezzo and Capocchio suffering from leprosy.
Canto XXX: Two mad sinners, Gianni Schicchi and Myrrha, dash up. Gianni Schicchi sinks his teeth into Capocchio’s neck and drags him off. The poets now see Master Adamo, a counterfeiter, and two liars suffering from fever, Sinon and Potiphar’s wife. Dante becomes absorbed by a vulgar argument between Sinon and Adamo but is promptly ashamed of himself when he is rebuked by Virgil for it.
Canto XXXI: Moving forward in the murky air, the poets hear a loud blast from the horn of Nimrod, who with other rebellious giants stand guard over Cocytus. Virgil flatters the only unchained giant, Antaeus, to place them down on the lake.
Canto XXXII: The poets walk on the outer region of the lake, known as Caïna. Here they see sinners who were violent against their kinsmen, including the brothers Napoleone and Alessandro, and Mordred. Then they enter the area known as Antenora, where Dante accidentally kicks the face of Bocca degli Abati. Further on, on the boundary between Antenora and Tolomea, Dante sees one head gnawing on another.
Canto XXXIII: Count Ugolino, who gnaws on the head of Archbishop Ruggieri, tells his story. He was betrayed by the Archbishop, who imprisoned him and his sons and grandson in the “tower of hunger”, where they starved to death. The Pilgrim then meets Friar Alberigo, who identifies himself on condition that Dante remove the ice from his eyes. Dante promises that if he does not, he will descend into the lake of ice. He does not remove the ice from Alberigo’s eyes, however, knowing full well that he will travel under Cocytus to Purgatory.
Canto XXXIV: In the region known as Judecca, the poets see sinners frozen entirely beneath the ice. At the center of the lake towers Lucifer, his gigantic batlike wings beating, his three faces (red, yellow, and black) each streaming with tears and blood, his three mouths chewing on Brutus, Cassius, and Judas Iscariot. The poets descend on Lucifer’s leg and turn upright when they pass the center of gravity. From there they climb up and eventually reach the earth’s surface and see the stars.