TheIliad opens with an expression of rage and frustration. The Trojan War has been raging for nine long years, with the Achaeans (Greeks) unable to break through the walls of Troy. King Agamemnon, who leads the Achaeans, has been forced to give up a valued prize, a woman he captured. This is no ordinary woman, but the daughter of a priest of Apollo; refusal to return her to her father brought on the wrath of Apollo in the form of a plague on the Greeks. Arrogant and high-handed, Agamemnon repairs his loss of honor by taking a prize from Achilles, a woman named Briseis whom Achilles values greatly. Achilles (who is at the beginning of the story as arrogant and high-handed as Agamemnon) resents the offense to his honor but is prevented by the goddess Athena from coming to blows with Agamemnon. Instead, he turns away and refuses to fight in the siege of Troy. To show Agamemnon who's more important, he asks the gods to allow the Trojans to defeat his own army—the Achaeans—until he returns to the fight. To bring this about, Achilles's mother, who is a goddess, secures the help of Zeus, the king of the gods.
The Achaean and Trojan armies march out onto the field to fight. But Paris, the Trojan prince who started the war by stealing the wife of Menelaus (brother of Agamemnon), proposes that it be settled by single combat between him and Menelaus. Menelaus agrees and a duel ensues. Just as Menelaus is about to defeat Paris, the goddess Aphrodite carries him back to Troy, and the battle recommences.
Athena helps the Achaean hero Diomedes in battle, enabling him to wound Aphrodite and Ares (Book 5), two of the gods helping Troy. Hector, a prince of Troy and the greatest Trojan warrior, briefly returns to the city to organize an appeal to the gods and fetch Paris back to the battlefield. The gods end the fighting for the day with a duel between Hector and Great Ajax, the second-strongest Achaean hero after Achilles. Ajax has the advantage but cannot kill Hector.
Both sides take a day off from fighting to bury their dead. The Achaeans take the opportunity to build a wall around their ships. When the fighting resumes the next day, Zeus forbids the other gods to interfere. He will control the war from now on. With Zeus's help, the Trojans push toward the Achaean ships. Agamemnon leads a brief rally for the Achaeans, but Hector pushes them all the way back to their new wall. Alarmed by the Trojan advance, Agamemnon offers Achilles many prizes, including the return of Briseis, to return to the battle. However, he offers no apology, and Achilles is not appeased.
Unable to sleep, the Achaean captains Odysseus and Diomedes make a daring night raid on the Trojan army, killing a number of Trojan allies. In the morning Agamemnon initially pushes the Trojans all the way back to the city. Zeus then turns the tide, causing most of the Achaean captains to be wounded. Many Achaeans fight valiantly, but Zeus empowers the Trojan fighters to break through the wall and threaten the Achaean ships. When Zeus takes his eye off the war for a bit, the sea-god Poseidon inspires the Achaeans to kill and wound many Trojans, holding them off the ships.
Hera devises a plan to distract Zeus. She seduces him after bribing the god Sleep to put him to sleep afterward. With Poseidon's help the Achaeans drive the Trojans back outside their wall. However, Zeus soon awakens and takes control again. He directs his son Apollo to strike fear into the Achaeans with Zeus's terrifying shield. As the Trojans reach the ships, Achilles's closest friend, Patroclus, begs him to return and save the Achaeans. Achilles is still too angry, but he lets Patroclus use his armor and chariot to make the Trojans think he has returned.
In Achilles's armor and chariot, Patroclus turns the tide of the battle, pushing the Trojans all the way back to their own city walls. However, he gets carried away and goes up against Hector, who kills him. Hector strips Achilles's armor from Patroclus but is driven back before he can claim the body. In a fit of pride, Hector fatefully puts on Achilles's armor. Great Ajax, Menelaus, and others hold off Hector and his troops. However, they cannot get Patroclus's body back to their camp until Achilles, having heard of his comrade's death, appears on the Achaean wall. The goddess Athena makes him glorious and terrifying. He frightens the Trojans enough for the Achaeans to retrieve Patroclus's body.
Now Achilles no longer cares about his quarrel with Agamemnon. All of his anger is focused on killing Hector. The next morning, his goddess mother brings him new armor (including the marvelous shield, the description of which is detailed in Book 18) made by the god of fire, and Zeus tells the gods they may intervene in the war. Achilles rages against the Trojans, slaughtering huge numbers. No mortal can stand against him. He sends the entire Trojan army retreating back to the city. Ashamed that he has led the Trojan army to defeat, Hector waits for Achilles outside the gates of Troy.
Despite his previous boasts, Hector loses his nerve and runs as Achilles approaches. After Achilles has chased him around the city three times, Athena tricks Hector into stopping. Achilles's divine armor protects him, but Hector is betrayed by the armor he is wearing, Achilles's old armor. Achilles kills Hector through a weak spot in the armor he knows so well. In his anger Achilles abuses Hector's body and drags it behind his chariot.
Over the next couple of days, Achilles and the Achaeans hold a funeral for Patroclus and compete in games in his honor. But Hector's family and the Trojans have no such comfort. Finally, Zeus decrees that Achilles must give Hector's body back. The god Hermes guides Priam, Hector's father, into the Achaean camp to appeal to Achilles. Achilles is moved by Priam's words and allows the Trojans time to bury Hector.