The Odyssey is written in dactylic hexameter. It opens in medias res, in the middle of the overall story, with prior events described through flashbacks or storytelling. This device is also used by later authors of literary epics, such as Virgil in the Aeneid, Luís de Camões in Os Lusíadas and Alexander Pope in The Rape of the Lock.
The first four books of the poem trace Telemachus' efforts to assert control of the household, and then, at Athena's advice, his efforts to search for news of his long-lost father. Then the scene shifts: Odysseus has been a captive of the beautiful nymph Calypso, with whom he has spent seven of his ten lost years. Released by the intercession of his patroness Athena, through the aid of Hermes, he departs, but his raft is destroyed by his divine enemy Poseidon, who is angry because Odysseus blinded his son, Polyphemus. When Odysseus washes up on Scherie, home to the Phaeacians, he is assisted by the young Nausicaä and is treated hospitably. In return, he satisfies the Phaeacians' curiosity, telling them, and the reader, of all his adventures since departing from Troy. The shipbuilding Phaeacians then loan him a ship to return to Ithaca, where he is aided by the swineherd Eumaeus, meets Telemachus, regains his household by killing the Suitors, and is reunited with his faithful wife, Penelope.
All ancient and nearly all modern editions and translations of the Odyssey are divided into 24 books. This division is convenient, but it may not be original. Many scholars believe it was developed by Alexandrian editors of the 3rd century BC. In the Classical period, moreover, several of the books (individually and in groups) were given their own titles: the first four books, focusing on Telemachus, are commonly known as the Telemachy. Odysseus' narrative, Book 9, featuring his encounter with the cyclops Polyphemus, is traditionally called the Cyclopeia. Book 11, the section describing his meeting with the spirits of the dead is known as the Nekuia. Books 9 through 12, wherein Odysseus recalls his adventures for his Phaeacian hosts, are collectively referred to as the Apologoi: Odysseus' "stories". Book 22, wherein Odysseus kills all the Suitors, has been given the title Mnesterophonia: "slaughter of the Suitors". This concludes the Greek Epic Cycle, though fragments remain of the "alternative ending" of sorts known as the Telegony.
Telegony aside, the last 548 lines of the Odyssey, corresponding to Book 24, are believed by many scholars to have been added by a slightly later poet. Several passages in earlier books seem to be setting up the events of Book 24, so if it were indeed a later addition, the offending editor would seem to have changed earlier text as well. For more about varying views on the origin, authorship and unity of the poem see Homeric scholarship.