The epic begins in the tenth year of the indecisive war with a domestic dispute among the Greeks. Agamemnon has been forced to return his war-prize mistress, the beautiful Chryseis, to her father, a priest of Apollo, in order to bring an end to a pestilence sent by the god to infect the Greek camp. Agamemnon agrees, but only after demanding, for his own use, Briseis, the war-prize mistress of his most powerful soldier, Achilles. Angered and humiliated by this arbitrary and arrogant act, Achilles pulls himself and his troops out of the war.

Throughout the epic, the gods and lesser deities take sides and even physically join in the battle, sometimes causing one side to prevail, sometimes the other. The head god Zeus, for instance, almost succeeds, through trickery, in getting the Greeks to go home, but Athene helps Odysseus to convince them to remain to fight. When, in Book III, Menelaus is about to kill his rival, Paris, Aphrodite (the goddess of love, an admirer of Paris) extricates the Trojan from danger. Zeus claims victory for the Greeks because Menelaus has defeated Paris, but Zeus’s wife Hera urges him to allow the war to go on. In Book V, the gods actually join in the fighting. Later, after a touching farewell scene between the greatest of the Trojan warriors, Hector, and his wife Andromache and tiny son Astyanax, Hector leads the Trojans out to battle. The Trojans are successful for a while and Agamemnon tries to get Achilles to return to the war, but the still-angry hero refuses. Meanwhile, on Mount Olympus, the home of the gods, Hera seduces her husband Zeus and during the great god’s sleep after lovemaking, Poseidon, encouraged by Hera, urges the Greeks on until Zeus wakes up and Poseidon has to withdraw. Once again the Trojans appear to be winning. Now Achilles’ close friend and companion Patroclus convinces the great hero to allow him to wear his armor and to enter the battle, thus causing the Trojans to believe that Achilles has returned to the war. The Trojans, thinking Achilles is back, retreat in terror, and Patroclus fights furiously until, with Apollo’s meddling help, Hector kills him. Distraught over his friend’s death, Achilles rejoins the battle after the blacksmith god Hephaistos makes him special armor. The gods join in and Achilles fights as no one had ever fought before, slaughtering any Trojan in his way. Eventually, with Athene’s help, he kills Hector and insults his body and the Trojans as a nation by dragging his victim’s body around the city walls. After the victory, the Greeks hold funeral games in honor of Patroclus, and in the final book, King Priam, in a deeply moving scene, comes to the Greek camp and begs Achilles to give him his son’s body. Achilles takes pity on the old man and releases the body. A twelve-day truce follows.