After an invocation to the Muse of poetry, the epic begins in medias res ("in the middle of things"). Odysseus has been gone from Ithaca for about 20 years — the first 10 spent fighting the Trojan War, the last 10 trying to get home.
Meanwhile, Odysseus' wife, Penelope, tries to fend off over 100 suitors who have invaded the royal palace, seeking her hand in marriage (and a chance of ruling Ithaca), and indulging in great amounts of food and wine at the hosts' expense. Telemachus, son of Odysseus and Penelope, is just coming of age (he is approximately 21) and is at a loss as to what to do about the suitors. Mother and son yearn for Odysseus' return.
The first four books deal with Telemachus' struggle (in fact, Odysseus does not appear in the epic until Book 5). A secondary plot in The Odyssey is Telemachus' coming of age, his own quest, which scholars sometimes refer to as the "Telemacheia."
The goddess Athena appears to the young prince in disguise and advises him to gather an assembly of the island's leaders to protest the invasion of the suitors. Soon after, he is to visit King Nestor of Pylos and King Menelaus of Sparta, old comrades of his father's, to gather from them any new of Odysseus.
At the assembly, the two leading suitors — the aggressive Antinous and the smooth-talking Eurymachus — confront the prince. They accuse Penelope of delaying too long in her choice of a new husband. Telemachus speaks well but accomplishes little at the assembly because the suitors are from some of the strongest families in the area and are impatient with Penelope's delays.
As Telemachus secretly sets off for Pylos and Sparta, the suitors plot to assassinate him. At Pylos, Telemachus learns little of his father but is encouraged to visit Sparta where King Menelaus reports that Odysseus is alive but held captive by the goddess nymph Calypso.
Homer leaves the story of Telemachus as the suitors are about to ambush his ship on its return to Ithaca. At Athena's urging, the gods have decided to free Odysseus from Calypso. Hermes, the messenger god, delivers the order to Odysseus' captor. Odysseus has spent seven years with the goddess, sleeping with her at night and pining for his home and family during the day. Calypso is a beautiful, lustful nymph who wants to marry Odysseus and grant him immortality, but he longs for Penelope and Ithaca. Reluctantly, Calypso sends Odysseus on his way.
Poseidon, the sea god, spots the wayfarer and, seeking revenge because Odysseus blinded Poseidon's son Cyclops, shipwrecks Odysseus on Phaeacia, which is ruled by King Alcinous. The Phaeacians, civilized and hospitable people, welcome the stranger and encourage him to tell of his adventures. Through Odysseus' narration, the reader goes back 10 years and hears his tale.
Known as "The Wanderings of Odysseus," this section is the most famous of the epic. At the end of the Trojan War, Odysseus and his men sail first to the land of the Cicones. The Greeks succeed in raiding the central city but linger too long and are routed by a reserve force. Hoping to sail directly home, the flotilla instead encounters a severe storm, brought on by Athena, that blows them far off course to the land of the Lotus-eaters. These are not hostile people, but eating the lotus plant removes memory and ambition; Odysseus is barely able to pull his men away and resume the journey.
Curiosity compels Odysseus to explore the land of the Cyclops, a race of uncivilized, cannibalistic, one-eyed giants. One of them, Polyphemus (also known simply as "Cyclops"), traps Odysseus' scouting party in his cave. To escape, Odysseus blinds the one-eyed monster, incurring the wrath of the giant's father, Poseidon.
Aeolus, the wind god, is initially a friendly host. He captures all adverse winds and bags them for Odysseus, who is thus able to sail within sight of Ithaca. Unfortunately, his men suspect that the bag holds treasure and open it while Odysseus sleeps. The troublesome winds blow the party back to Aeolus, who wants no more to do with them, speculating that they must be cursed by the gods.
The next hosts, the cannibalistic Laestrygonians, sink all the ships but Odysseus' in a surprise attack. The remaining Greeks reach Aeaea, home of the beautiful enchantress Circe, who turns several of them into pigs. With advice from Hermes, Odysseus cleverly defeats Circe and becomes her lover. She lifts the spell from his men and aids in the group's eventual departure a year later, advising Odysseus that he must sail to the Land of the Dead. There, he receives various Greek heroes, a visit from his own mother, and an important prophecy from the seer Tiresias. Odysseus resumes his journey.
Barely surviving the temptations of the Sirens' songs and an attack by a six-headed monster named Scylla, Odysseus and his crew arrive at the island of the Sungod Helios. Despite severe warnings not to, the men feast on the cattle of the Sungod during Odysseus' brief absence. Zeus is outraged and destroys the ship as the Greeks depart, killing all but Odysseus, who is washed ashore at Calypso's island, where he stays until released seven years later.
The story of his adventures finished, Odysseus receives the admiration and gifts of the Phaeacians who follow their tradition of returning wayfaring strangers to their homelands by sailing him to Ithaca. Meanwhile, Athena helps Telemachus avoid the suitors' ambush and arranges for him to meet his father at their pig farm not far from the palace.
Reunited with his son and with the assistance of Athena and his faithful swineherd Eumaeus, Odysseus returns to his home palace disguised as a beggar. For the time, he resists striking back at the suitors who insult and assault him. Penelope seems at least suspicious that he is her husband, but it is Eurycleia, a loyal nurse who cared for Odysseus when he was a child, who has no doubt of his identity as she discovers an old scar on his leg when she bathes him.
Penelope arranges a contest, vowing to wed any man who can string the great bow of Odysseus and shoot an arrow through a dozen axes as he used to do. The suitors all fail; only Odysseus himself can perform the feat. With deft planning and more help from Athena, he and Telemachus and two faithful herdsmen slaughter the suitors. Odysseus and Penelope are reunited, as are Odysseus and his aging father, Laertes. Athena makes peace with the suitors' vengeful friends and families, avoiding civil war. Odysseus is home at last.