The Tombs of Atuan

Tenar, a girl born on the Kargish island of Atuan, is believed to be the reincarnation of the high priestess of the tombs of Atuan. She is taken from her family when she turns five, and goes to the Tombs. Her name is taken from her in a ceremony, and she is referred to as "Arha", or the "Eaten One", after being consecrated to the service of the "Nameless Ones" at the age of six with a ceremony involving a symbolic sacrifice. She moves into her own tiny house, and is given a eunuch servant, Manan, with whom she develops a bond of affection.
Arha's childhood and youth are lonely; her only friends are Manan and Penthe, a priestess her own age. She is trained in her duties by Thar and Kossil, elderly priestesses of the two other major deities. Thar tells her of the Undertomb and the Labyrinth beneath the Tombs, teaching her how to find her way around them in the darkness. She tells of the treasure hidden within the Labyrinth, which wizards from the Archipelago have tried to steal. When Arha asks about the wizards, Thar tells her that they are unbelievers who can work magic.
When she turns fourteen, Arha assumes all the responsibilities of her position, becoming the highest-ranked priestess in the Tombs. As part of her duties, she is required to execute prisoners sent to the Tombs by the God-King of the Kargad lands; she has them killed by starvation, an act which haunts her. After Thar dies of old age, Arha becomes increasingly isolated: although stern, Thar had been fair to her; Kossil despises Arha and feigns belief in the Nameless Ones.
Arha's routine is disrupted by her discovery of the wizard Ged (the protagonist of A Wizard of Earthsea) in the Undertomb, the main hub of the Tombs. As Ged advances into the Labyrinth, she traps him behind a locked door and through a peephole sees him unsuccessfully attempt to open the door with a spell. Ged eventually collapses out of exhaustion, and Arha has him chained while debating his fate.
After questioning him, she learns that he has come to the Tombs to retrieve one half of the long-lost Ring of Erreth-Akbe, a magical artifact broken centuries earlier which is inscribed with nine Runes of Power; the breaking caused the Bond-Rune, necessary for peace in Earthsea, to be forgotten. Ged unknowingly received his half of the Ring during the events of A Wizard of Earthsea, and a dragon later told him what it was. Arha is enamored by Ged's tales of the outside world and delays executing him, instead sneaking him food and water.
Kossil learns of Ged's existence, forcing Arha to promise that Ged will be sacrificed to the Nameless Ones; however, she realizes that she cannot go through with it, instead instructing Manan to dig a false grave in the Undertomb; she hides Ged in the Treasury, where neither Manan nor Kossil can enter. As she departs the Treasury, Ged thanks her using her true name—Tenar.
Arha and Kossil have a public argument in which Kossil declares that the Nameless Ones no longer have power while Arha curses her in their name. Realizing that Kossil will now be determined to kill her, she heads to the labyrinth and sees Kossil exhuming Ged's false grave. Evading her, Arha goes to the Treasury and confesses everything to Ged, who has found the other half of Erreth-Akbe's ring. He tells Arha that she must either kill him or escape with him, and says that while the Nameless Ones demand her service, they neither give nor create anything in return. He tells her his true name, reciprocating her trust.
Manan intervenes by attempting to attack Ged, but falls to his death in a pit as the tombs begin to collapse in on themselves; Ged holds off their destruction until they are able to escape to the surface. Arha reverts to calling herself Tenar as she and Ged travel across Atuan to the coast where his boat is hidden, intending to travel to present the Ring at Havnor. While waiting for the tide, she feels an urge to kill Ged for destroying her life, but realizes while gazing at him that she has no anger left. Ged and Tenar sail to Havnor, where they are received in triumph.