Note: Book numbers are in parentheses and come before the synopsis of the book.
After an invocation to the Muses, the story launches in medias res towards the end of the Trojan War between the Trojans and the besieging Greeks. Chryses, a Trojan priest of Apollo, offers the Greeks wealth for the return of his daughter Chryseis, a captive of Agamemnon, the Greek leader. Although most of the Greek army is in favour of the offer, Agamemnon refuses. Chryses prays for Apollo's help, and Apollo causes a plague throughout the Greek army.
After nine days of plague, Achilles, the leader of the Myrmidon contingent, calls an assembly to solve the plague problem. Under pressure, Agamemnon agrees to return Chryseis to her father, but also decides to take Achilles's captive, Briseis, as compensation. Angered, Achilles declares that he and his men will no longer fight for Agamemnon, but will go home. Odysseus takes a ship and brings Chryseis to her father, whereupon Apollo ends the plague.
In the meantime, Agamemnon's messengers take Briseis away, and Achilles asks his mother, Thetis, to ask Zeus that the Greeks be brought to the breaking point by the Trojans, so Agamemnon will realise how much the Greeks need Achilles. Thetis does so, Zeus agrees, and sends a dream to Agamemnon, urging him to attack the city. Agamemnon heeds the dream but decides to first test the morale of the Greek army by telling them to go home. The plan backfires, and only the intervention of Odysseus, inspired by Athena, stops a rout.
Odysseus confronts and beats Thersites, a common soldier who voices discontent at fighting Agamemnon's war. After a meal, the Greeks deploy in companies upon the Trojan plain. The poet takes the opportunity to describe the provenance of each Greek contingent. When news of the Greek deployment reaches king Priam, the Trojans too sortie upon the plain. In a similar list to that for the Greeks, the poet describes the Trojans and their allies.
The armies approach each other on the plain, but before they meet, Paris offers to end the war by fighting a duel with Menelaus, urged by his brother and head of the Trojan army, Hector. While Helen tells Priam about the Greek commanders from the walls of Troy, both sides swear a truce and promise to abide by the outcome of the duel. Paris is beaten, but Aphrodite rescues him and leads him to bed with Helen before Menelaus could kill him.
Pressured by Hera's hatred of Troy, Zeus arranges for the Trojan Pandaros to break the truce by wounding Menelaus with an arrow. Agamemnon rouses the Greeks, and battle is joined. In the fighting, Diomedes kills many Trojans and defeats Aeneas, whom again Aphrodite rescues, but Diomedes attacks and wounds the goddess. Apollo faces Diomedes, and warns him against warring with gods. Many heroes and commanders join in, including Hector, and the gods supporting each side try to influence the battle. Emboldened by Athena, Diomedes wounds Ares and puts him out of action.
Hector rallies the Trojans and stops a rout; the Greek Diomedes and the Trojan Glaukos find common ground and exchange unequal gifts. Hector enters the city, urges prayers and sacrifices, incites Paris to battle, bids his wife Andromache and son Astyanax farewell on the city walls, and rejoins the battle. Hector duels with Ajax, but nightfall interrupts the fight and both sides retire. The Greeks agree to burn their dead and build a wall to protect their ships and camp, while the Trojans quarrel about returning Helen. Paris offers to return the treasure he took, and give further wealth as compensation, but without returning Helen, and the offer is refused.
