Maia is set in the Beklan Empire, the same fantasy world as Adams's 1974 novel Shardik. Although published ten years after Shardik, Maia is a loose prequel whose events take place about a dozen years earlier. A few characters appear in both books.
Maia is a beautiful teenage peasant girl who is sold into slavery. Amidst colourful, boldly drawn characters, she is drawn (sometimes unwillingly or even unknowingly) into many adventures and machinations: ritual dances, flooding rivers, espionage, politics, and war. Some scenes, particularly during Maia's enslavement, include moderately explicit sexual and sado-masochistic elements. Nevertheless, she survives the decadence and danger with an impulsive, innocent sense of courage and enterprise. Maia ends with the sort of quotidian, pastoral, familial scene (in Maia's memory and expectation of returning home) which commonly rewards the positive characters in Adams's works.
The morality of slavery is discussed among the characters throughout the book, and a civil war is fought in part to restrict the actions of slavers and limit the number of slaves in the Beklan Empire.
Maia, at 15, lives in the Beklan Empire's province of Tonilda with her mother Morca, her three younger sisters, and her stepfather, Tharrin. Their small, poor farm is on the edge of Lake Serrelind, and Maia tends to shirk her chores by swimming in the lake all day. Although Morca is pregnant with Tharrin's child, he secretly seduces Maia.
When Morca discovers the affair, she is doubly embittered and sells Maia to agents of the slave-dealer Lalloc. Maia is almost raped by Genshed, one of Lalloc's employees but is saved by Occula, a black slave girl. Maia and Occula become very good friends and even lovers. To avoid debasement by being bundled in with a detachment of more ordinary slaves, Occula enlists Maia in frightening their captors with apparent supernatural powers. The two girls are sent to the city of Bekla.
Occula relates her own past: her father, a jewel-merchant, brought her across the desert to Bekla. They were received by Fornis, a noblewoman whom a coup would shortly elevate to the priestess-like status of "Sacred Queen". Fornis had Occula's father murdered and his emeralds incorporated into the Sacred Queen's crown. Occula was to be killed as well, but the household steward saw a chance to profit by selling the girl as a slave; since then, she has been employed in prostitution.
Adams outlines Bekla's political situation in several chapters that bypass Maia. The "Leopard" faction led by the High Baron Durakkon, Fornis, the Lord General Kembri, and the High Counsellor Sencho came to power by ceding Suba, a western province, to the neighbouring kingdom of Terekenalt. They legalised slavery, and the capital's finances are now heavily based on taxation of it, including farms for breeding slaves as well as the enslavement of freeborn people such as Maia and Occula. The Beklan army's central authority has largely withdrawn from the provinces unless paid to come enforce the law. Pockets of rebellion have sprung up around the empire.
High Counsellor Sencho is the spymaster of the Beklan Empire. He buys both Maia and Occula as "bed-slaves". Terebinthia, the woman in charge of Sencho's household, supervises and trains them. At intervals, a peddler named Zirek visits and exchanges cryptic conversations with Occula.
Beautiful, young, and fun-loving, Maia shows promise of going far, and finds some professional satisfaction in providing Sencho's decadent pleasures. She is even surprised that she enjoys the spectacle when a fellow bed-slave, the tempestuous Meris, is whipped and sold for dereliction of duty.
Terebinthia rents out the girls to other rich and powerful men. Using this means of contact, Lord General Kembri secretly enlists Maia and Occula as agents and charges Maia with gaining the trust of Bayub-Otal, the dispossessed heir to Suba and a potential ally of the rebels. Bayub-Otal is the son of a dancer nicknamed "Nokomis" ("dragonfly") and the baron of a neighbouring province, whose jealous wife arranged Nokomis' death when Bayub-Otal was a boy.
When Sencho becomes drastically ill, he comes to depend almost solely on Occula's intense caretaking. During a garden party, Occula lures Sencho out of sight of everyone else and signals her rebel confederates (by implication Zirek and Meris) to stab Sencho to death.
Maia and Occula are imprisoned in the Great Temple on suspicion of colluding in Sencho's murder. Queen Fornis takes Maia from the temple priests. As Maia fails to satisfy her sexual needs, Fornis gives her to Kembri; Maia seizes on this chance to interest the queen in Occula, hoping to save her friend from execution.
Kembri sends Maia to Bayub-Otal with a cover story of having escaped from the temple. Bayub-Otal takes her with him as he secretly makes his way back to Suba. Maia learns that one reason for his extraordinary standoffish respect for her is that she looks (and dances) like his dead mother, Nokomis, who is still revered throughout the province. Bayub-Otal hopes to use the resemblance to rally Suban patriotism on behalf of an alliance with Terekenalt.
At the rallying site, Maia falls passionately in love with the handsome young Zen-Kurel, an officer of Terekenalt. Zen-Kurel accepts her invitation to bed, but leaves quickly because of a surprise attack scheduled for that very night. The River Valderra, the boundary between the two countries, is thought to be uncrossably swift and rocky, but the Terekenalters plan to ford it with heavy ropes and strong men, thus surprising the detachment of Tonildan soldiers guarding the other side.
In hopes of saving her fellow Tonildans' lives as well as her lover's, Maia swims the river by herself. Despite serious wounds, she warns the Beklan commander and thwarts the Terekenalter and Suban invasion.
Maia returns to Bekla, freed and celebrated as the luck of the city, a great heroine whom the soldiers vote a house, money, and property. She gains an informal title as the "Serrelinda" after Lake Serrelind. Hoping to reunite with Zen-Kurel, she takes no lovers, despite expectations that she will find a rich husband or become an expensive courtesan. Her popularity and single status bring her under threat from Fornis, who is resisting pressure to retire as Sacred Queen; since the position is filled by popular acclaim, Maia is an obvious rival despite not wanting the crown.
Maia sees her stepfather, Tharrin, dragged into Bekla as a rebel informant. He is condemned to be sacrificed by the Queen. Maia does her best to free him, but Fornis foils her plan and causes his death. However, during Tharrin's last conversation with Maia, he reveals to her that Morca had not been her real mother. A pregnant girl had fled to Morca's cottage and died there in childbirth; Maia deduces she is the daughter of Nokomis' younger sister.
In grief at Tharrin's death, Maia makes a desperate attempt to kill Fornis, but is thwarted by Occula, who was indeed inducted into the queen's household. Occula intends to take her own revenge on Fornis when the time is right; meanwhile she is performing the sort of sado-masochistic services of which Maia had been incapable and which show how deranged Fornis can be.
As civil war breaks out in the city, Maia learns that Anda-Nokomis and Zen-Kurel have been brought to Bekla as prisoners. In flight from Fornis' murderous fury, Maia frees the two men, and with them and Zirek and Meris (who have been hiding since assassinating Sencho), she flees Bekla.
The former prisoners are bitterly angry at Maia for betraying them at the Valderra, which she had idealistically considered an attempt to save their lives. Nevertheless, they agree to return with her to Suba or Terekenalt.
Maia and her companions recover on a remote farm, then travel for a time with rebel freebooters. Meris, always a troublemaker, gets herself killed by one of them. Maia gradually regains Zen-Kurel's and Anda-Nokomis' trust by her sincere efforts to help them. After an arduous boat escape from the Beklan Empire to Terekenalt, Anda-Nokomis is killed and Maia receives a marriage proposal from the man she loves most.
Two years later, Maia (with her little son) visits the capital of her new country and by chance meets Occula. Occula describes at length how she killed Fornis, aided by supernatural forces. She tells Maia that the rebels succeeded in overthrowing the Leopards' regime.
The story ends with Maia refusing Occula's plea to go back to Bekla; she would rather help Zen-Kurel and his father manage their farm.
Many Beklan gods are associated with different provinces of the empire. The pantheon includes Lespa of the Stars, Frella-Tiltheh the Inscrutable (Bekla City), Shardik the Bear (Ortelga), Shakkarn the Goat, Canathron the Winged Serpent (Lapan), Cran (a fertility and harvest god), and Airtha of the Diadem (a sky-goddess and Cran's consort).
Kantza-Merada is the goddess of Occula's homeland, Silver Tedzhek; Occula invokes her with a ritual chant historically associated with the Sumerian goddess Inanna. The same chant appears in Shardik with Inanna's name intact.
Much as Adams had invented words of the Lapine language for the rabbits of Watership Down, he employs some "Beklan" vocabulary for honorifics, natural objects, and sexual terms; the last "allows adults to leave the book within reach of children." Some are also used in Shardik.
The New Yorker quipped that though Maia's career as a Playboy Bunny was reminiscent of Watership Down, she seemed more like a fish, and her swimming "changes... much more than her career". It said "Mr. Adams's artistry distinguishes his work from those didactic fantasies which border on science fiction"; instead the aim was entertainment, as shown in the elaborate settings, and the reader has no reason to put the book down.