The backstory is revealed as the book progresses, and also elaborated in the Appendices and in The Silmarillion, published after Tolkien's death.

The backstory begins thousands of years before the action in the book, with the rise of the eponymous Lord of the Rings, the Dark Lord Sauron, a malevolent incarnated immortal spiritual being possessed of great supernatural powers, later the ruler of the dreaded realm of Mordor. At the end of the First Age of Middle-earth, Sauron survived the catastrophic defeat and exile of his master, the ultimate evil figure, Morgoth (who was formerly counted as one of the Valar, the angelic Powers of the world). During the Second Age, Sauron schemed to gain dominion over Middle-earth. In the guise of "Annatar" or Lord of Gifts, he aided the Elven-smiths of Eregion in the forging of magical rings which conferred various powers and effects on their wearers. The most important of these were nineteen, called the Rings of Power or Great Rings.

However, he then secretly forged a Great Ring of his own, the One Ring, by which he planned to enslave the wearers of the other Rings of Power. This plan failed when the Elves became aware of him and took off their Rings. Sauron then launched a war during which he captured sixteen and distributed them to lords and kings of Dwarves and Men; these Rings were known as the Seven and the Nine respectively. The Dwarf-lords proved too tough to enslave although their natural desire for wealth, especially gold, increased; this brought more conflict between them and other races. The Men who possessed the Nine were slowly corrupted over time and eventually became the Nazgûl or Ringwraiths, Sauron's most feared servants. Sauron failed to capture Three, and these remained in the possession of the Elves (Celebrimbor, leader of the Elven-smiths, had forged them independently of Sauron). The war ended as the Men of the great island-nation of Númenor helped the besieged Elves, and Sauron's forces retreated.


Over 1500 years later, the Númenóreans sent a great force to overthrow Sauron. Deserted by his minions, Sauron surrendered and was taken to Númenor as a "prisoner". Though taken as a prisoner, such was his cunning and the strength of his will that in no time he was their King Ar-Pharazôn's closest counsellor. Sauron started to poison the minds of the Númenóreans against the Valar. He deceived Ar-Pharazôn into invading their lands, the Undying Lands, to gain the immortality of the Elves (many of the Elves had previously lived there, and many still did). However, upon reaching their destination, the King and his army were buried by a landslide. The Valar called upon Ilúvatar (God), who opened a great chasm in the sea, destroying Númenor, and removed the Undying Lands from the mortal world. The destruction of Númenor destroyed Sauron's fair and handsome physical body, but his spirit returned to Mordor and assumed a new form — black, burning hot (though he was not on fire), and terrible. Some Númenóreans (called the Faithful, for they did not join Ar-Pharazôn's expedition) also managed to escape to Middle-earth. They were led by Elendil and his sons Isildur and Anárion.

Over 100 years later, Sauron launched an attack against the Númenórean exiles. Elendil formed the Last Alliance of Elves and Men with the Elven-king Gil-galad. They marched against Mordor, defeated Sauron on the plain of Dagorlad, and besieged his stronghold Barad-dûr, at which time Anárion was slain. After seven years of siege, Sauron himself was ultimately forced to engage in single combat with the leaders. Gil-galad and Elendil were killed as they fought with Sauron, and Elendil's sword, Narsil, broke beneath him. However, Sauron's body was also overcome and slain, and Isildur cut the One Ring from Sauron's hand with the hilt-shard of Narsil; when this happened, Sauron's spirit fled and did not reappear in his terrible form for many centuries. Isildur was advised to destroy the One Ring by the only effective means — casting it into the volcanic Mount Doom where it was forged — but, attracted to its beauty, he refused and kept it as weregild (compensation) for the deaths of his father and brother.

So began the Third Age of Middle-earth. Two years later, Isildur and his soldiers were ambushed by a band of Orcs at what was eventually called the Disaster of the Gladden Fields. While the latter were almost all killed, Isildur escaped by putting on the Ring — which made mortal wearers invisible. However, the Ring slipped from his finger while he was swimming in the great River Anduin; he was seen and killed by Orc-arrows, and the Ring was lost for two millennia. It was then found by chance by a hobbit named Déagol. His relative and friend Sméagol strangled him for the Ring and was banished from his home by his maternal grandmother. He fled to the Misty Mountains where he slowly withered and became a disgusting, slimy creature called Gollum.

In The Hobbit, set 60 years before the events in The Lord of the Rings, Tolkien related the story of the seemingly accidental finding of the Ring by another hobbit, Bilbo Baggins, who took it to his home, Bag End. The tale related in The Hobbit was written before The Lord of the Rings, and it was only later that the author developed Bilbo's magic ring into the "One Ring". Neither Bilbo nor the wizard, Gandalf, were aware at this point that Bilbo's magic ring was the One Ring, forged by the Dark Lord Sauron.

The Lord of the Rings takes up the story about 60 years after the end of The Hobbit. It was first published in three volumes - The Fellowship of the Ring, The Two Towers and The Return of the King. The main story is divided into six books (two for each volume), successively numbered by Roman numerals. There is also a Foreword and a Prologue in The Fellowship of the Ring and six Appendices at the end of The Return of the King.

The Foreword of the Second Edition includes a dedication to American fans and a statement that the book is not an allegory, as some of its readers had already supposed. The Prologue includes a few sections providing backstory on the identity and customs of Hobbits, and a brief synopsis of The Hobbit.

Book I in The Fellowship of the Ring begins with Bilbo's hundred-and-eleventh birthday party, and his subsequent disappearance using his magic ring. Leaving to journey once more, he left much of his belongings, including the ring, to his cousin and adoptive heir Frodo Baggins.

After seventeen years of investigating, their old friend Gandalf the Grey revealed that the ring was in fact the One Ring, the instrument of Sauron's power, which the Dark Lord had been searching for most of the Third Age, and which corrupted others with desire for it and the power it held.

Sauron sent the sinister Ringwraiths, in the guise of riders in black, to the Shire, Frodo's native land, in search of the Ring. Frodo escaped, with the help of his loyal gardener Samwise "Sam" Gamgee and three close friends, Meriadoc "Merry" Brandybuck, Peregrin "Pippin" Took, and Fredegar "Fatty" Bolger. While Fatty acted as a decoy for the Ringwraiths, Frodo and the others set off to take the Ring to the Elven haven of Rivendell. They were aided by the enigmatic Tom Bombadil, who saved them from Old Man Willow and took them in for a few days of feasting, rest, and counsel. At the town of Bree, Frodo's party was joined by a man called "Strider", who was revealed, in a letter left by Gandalf at the local inn for Frodo, to be Aragorn, the heir to the kingships of Gondor and Arnor, two great realms founded by the Númenórean exiles. Aragorn led the hobbits to Rivendell on Gandalf's request. However, Frodo was gravely wounded by the leader of the Ringwraiths at the hill of Weathertop. With the help of his companions and the Elf-lord Glorfindel, Frodo managed to enter Rivendell's borders by crossing the Ford of the river Bruinen. Here he engaged in a stand-off with the Ringwraiths, but they were swept away by an enchantment of the river when they entered its waters. The book ends with Frodo losing consciousness.

Book II in The Fellowship of the Ring reveals that Frodo managed to recover under the care of the Half-elven lord Elrond, master of Rivendell. The hobbits also learned that Sauron's forces can only be resisted if Aragorn took up his inheritance and fulfilled an ancient prophecy by wielding the sword Andúril, which had been forged anew from the shards of Narsil, the sword that cut the Ring from Sauron's finger in the Second Age. Frodo also meets Bilbo, now living in retirement, and sees Elrond's daughter Arwen, Aragorn's betrothed.

Later, much of the story's exposition is given during a high council, attended by representatives of the major races of Middle-earth; Elves, Dwarves, and Men, and presided over by Elrond. Gandalf told them of the emerging threat of Saruman, the leader of the Order of Wizards, who wanted the Ring for himself and had imprisoned him for a time. After pondering several choices, the Council decided that the only course of action that could save Middle-earth was to destroy the Ring by taking it to Mordor and casting it into Mount Doom, where it was forged.

Frodo volunteered for the task, and a "Fellowship of the Ring" was formed to aid him — which consisted of Frodo, his three Hobbit companions, Gandalf, Aragorn, Boromir of Gondor, Gimli the Dwarf, and Legolas the Elf. Their journey took them through plains and over mountains, and ultimately the Mines of Moria, where they were followed by the wretched creature Gollum, whom Bilbo had met in the Goblin-caves of the Misty Mountains years before. (The full tale of their meeting is told in The Hobbit.) Gollum long possessed the Ring before it passed to Bilbo. Earlier in Book I, Gandalf explained that Gollum belonged to a people "of hobbit-kind" before he came upon the Ring, which corrupted him. A slave to the Ring's evil power, Gollum desperately seeked to regain his "Precious". As they proceeded through the Mines, Pippin unintentionally betrayed their presence and the party was attacked by Orcs. Gandalf battled a demon of fire and darkness, the Balrog, and fell into a deep chasm, apparently to his death. Escaping from Moria, the Fellowship, now led by Aragorn, went to the Elven realm of Lothlórien. Here, the Lady Galadriel showed Frodo and Sam visions of the past, present, and future. Frodo also perceived the Eye of Sauron, a metaphysical expression of Sauron himself, and Galadriel was tempted by the Ring. By the end of the first volume, after the Fellowship had travelled along the great River Anduin, Frodo decided to continue the trek to Mordor on his own, largely due to the Ring's growing influence on Boromir; however, the faithful Sam insisted on going with him.

The second volume, The Two Towers, deals with two parallel storylines in each of its books. Book III details the exploits of the remaining members of the Fellowship who aid the country of Rohan in its war against Saruman. At the start of the book, the Fellowship was further scattered; Merry and Pippin were captured by Sauron and Saruman's orcs, Boromir was mortally wounded defending them, and Aragorn and the others went off in pursuit of their captors. The three met Gandalf, who had returned as "Gandalf the White"; he had defeated the Balrog at the cost of his life, but had been sent back to Middle-earth, with enhanced powers, to aid the forces of good. Gandalf, Aragorn, Legolas and Gimli helped defeat Saruman's armies at the Battle of the Hornburg while Saruman himself was cornered by the tree-like Ents and Huorns, accompanied by Merry and Pippin, who have escaped from captivity. The two groups were reunited in the aftermath of the battle. After Saruman refused to repent of his folly, Gandalf cast him from the Order of Wizards.

Book IV tells of Frodo and Sam's exploits on the way to Mount Doom. They managed to capture and "tame" Gollum, who showed them a way to enter Mordor secretly (as opposed to the Black Gate), albeit through the dreaded valley of Minas Morgul. At the end of the volume, Gollum betrayed Frodo to the great spider, Shelob, and though he survived, he was captured by orcs. Meanwhile, Sauron launched an all-out military assault upon Middle-earth, with the Witch-king (leader of the Ringwraiths) leading a fell host from Minas Morgul into battle against Gondor, in the War of the Ring.

In the third volume, The Return of the King, the further adventures of Gandalf, Aragorn and company are related in the first book of the volume, while Frodo and Sam's are related in the second, as with The Two Towers. As told in Book V, the Fellowship assisted in the final battles against the armies of Sauron, including the siege of the tower-city of Minas Tirith in Gondor and the climactic life-or-death battle before the Black Gate of Mordor, where the alliance of Gondor and Rohan fought desperately against Sauron's armies in order to distract him from the Ring, and hoped to gain time for Frodo to destroy it.

In Book VI, Sam rescued Frodo from captivity. After much struggle, they finally reached Mount Doom itself, tailed by Gollum. However, the temptation of the Ring proved too great for Frodo and he claimed it for himself. Subsequently, Gollum struggled with him and managed to bite the Ring off. Crazed with triumph, Gollum slipped into the fires of the mountain, and the Ring was destroyed.

Thus, Sauron was banished from the world and his realm ended. Aragorn was crowned king and married Arwen, the daughter of Elrond. However, all was not over, for Saruman had managed to escape his captivity and enslave the Shire. Though he was overthrown by the Hobbits and the four heroes helped to restore order and beautify the land again, it was not the same Shire that they left. At the end, Frodo remained wounded in body and spirit and sailed west accompanied by Bilbo over the Sea to the Undying Lands, where he could find peace.

The Appendices contain much material concerning the timeline of the story, and information on the peoples and the languages of Middle-earth. Notably, Arwen, physically absent for much of the book, is dealt with in full here; her backstory and future with Aragorn are related.

According to Tolkien's timeline, the events depicted in the story occurred between Bilbo's announcement of his birthday party, and Sam's re-arrival to Bag End on . Most of the events portrayed in the story occur in 3018 and 3019, with Frodo heading out from Bag End on , and the destruction of the Ring six months later on .

For character information see: List of Middle-earth characters