Set in the Australian Outback from the 1910s through the mid-20th century, the novel opens in July 1933 at the Pleasant Skies Psychiatric Hospital. Anna, a 32-year-old wife and mother of twin daughters, has been committed after attacking her English cousin Rose and threatening Rose's infant son Joshua. Rose, visibly pregnant, visits to make peace, but Anna slaps her twice and curses her in Danish before attendants drag her away. The scene frames the central tragedy: Anna allowed something extraordinary for Rose's benefit, and the consequences destroyed her world.
The narrative returns to December 1918. Anna grows up on Sugar Alexandria, a remote cattle station outside Esperance, Australia. Having lost her mother during childbirth and her twin sister Blessing to pneumonia at age five, she is raised by Yarrajan, her Aboriginal nanny and surrogate mother. Each summer, Rose, who has a birth defect affecting her legs and uses a cane, travels from London to stay at the station. The cousins forge a bond closer than sisters, playing in their neighbor Cassandra Fancy's garden alongside Liam Herdsman, a boy who is deaf and has an intellectual disability. Rose mentors the wild, motherless Anna and becomes her emotional anchor.
At Anna's brother Christian's wedding, Rose meets James Ragnar Shahan, an Irish-Australian war veteran and aspiring pianist. They share an intense connection and kiss before being separated. Rose gives only her middle name, Charlotte, and keeps the Celtic ring James places on her finger. Soon after, Rose returns to London for an arranged marriage, leaving Anna devastated.
Anna's loneliness intensifies her undiagnosed mental illnesses: She hears voices, sees a spectral woman named Genevieve, and converses with her dead mother and sister at a secret shrine in the bush. Obsessed with James, Anna deliberately gets him drunk, seduces him, and falsely claims she is pregnant. James, who had been accepted to the Royal Academy of Music in London, cancels his plans and marries her out of moral obligation. When the lie is discovered, he stays, trapped by his vows. Anna does not conceive for another 10 years.
Over the following decade, James transforms from a cultured musician into a resentful station owner while Anna's condition worsens. She hallucinates shadow people, takes on her dead mother's persona during fits of rage, and builds a bizarre shrine adorned with a goose-feathered crown. An unmarked grave in the family burial plot haunts them both: Anna insists she shot a wolf, but the truth is far darker.
In November 1929, Rose telegrams from London. Her husband Paul has died by suicide after the stock market crash, and she asks to return to Sugar Alexandria. Overjoyed, Anna pressures James into converting a windmill into Rose's home, even trading his cherished family piano for furniture without his consent. When Rose arrives, James recognizes her as Charlotte from the wedding. Rose recognizes him too, but neither tells Anna. Yarrajan warns Anna of a prophetic dream foretelling trouble, but Anna dismisses the omen.
Anna devotedly nurses the depressed Rose back to health. As the cousins restore Cassandra Fancy's garden and Rose begins painting portraits, the suppressed attraction between James and Rose intensifies. James gives Rose weekly piano lessons and secretly draws intimate portraits of her at the Barracuda Hut, a fisherman's cabin on a nearby island.
Anna then proposes a shocking idea: James should sleep with Rose to give her a baby, which would fulfill Rose's dream and bind her to Sugar Alexandria forever. James refuses. Over months, Anna escalates her campaign, refusing domestic duties, withholding intimacy, and delivering a devastating taunt echoing his father's words that James is not a real man. Worn down and burning with long-suppressed desire, James capitulates. He removes his wedding ring, goes to Rose's windmill, and they make love through the night.
Unable to return to a platonic relationship, James and Rose begin a secret affair. Rose becomes pregnant, and they tell the town a fabricated story about an absent father. Anna is overjoyed, believing her plan has succeeded, though insecurity begins to surface. James confesses to Rose that he never loved Anna and wants to leave. Yarrajan deduces the affair and gives James an ultimatum: tell Anna, or she will.
Rose gives birth to a healthy boy named Joshua during a violent storm, with Anna and Yarrajan as midwives. The affair continues, and Rose becomes pregnant again. James and Rose attempt to flee but turn back when Rose insists on telling Anna in person. James repeatedly loses his nerve. Eventually Liam, who has observed the lovers at the Barracuda Hut, tells Anna what he has seen and directs her to the cabin.
Anna discovers James's drawings and love letters at the Barracuda Hut. She confronts James in his distillery; he confirms he loves Rose and wants a divorce. Anna strikes him with a mallet, then storms into Rose's windmill with a knife, cycling between her own identity and those of her dead mother and sister. Urged on by hallucinations, she stabs Rose twice in the neck and seizes baby Joshua, carrying him toward a refuse fire. A stockman grabs her from behind while James catches the baby. Anna is restrained until she passes out and committed to Pleasant Skies.
James and Rose flee, entrusting the twins to Yarrajan. At the hospital, Anna endures shock therapy, ice-water treatments, and abuse from staff. Through therapy with Dr. Octavia, she makes critical breakthroughs: She acknowledges she killed not a wolf but Callum McTavish, a war veteran. She accepts her hallucinated companions are not real. She learns her mother did not die in childbirth but had the same illnesses and died at Pleasant Skies years later. Declared mentally unfit for trial, Anna signs the divorce papers James brings after he explains he never wanted to marry her. The narrative then circles back to its opening scene: Rose's visit to the hospital, though violent, proves a therapeutic breakthrough for Anna.
James and Rose marry in Cong, County Galway, Ireland. They have two more children, and James builds a concert career touring Europe and Australia. Together they found Liam's Lyrics, a school teaching people who are deaf to play instruments through vibration and image association.
After a year at Pleasant Skies, Anna is released and rebuilds her life. She marries Flossy McKay, a neighboring station owner, and together they expand Sugar Alexandria. Anna manages her illnesses with medication and the coping strategies Dr. Octavia taught her. During James's Australian tour, she secretly attends his concert and is moved to tears by his final composition,
The Consequence of Anna.
Decades later, after Flossy's death, Joshua, now a physician, visits elderly Anna and assures her his mother has long forgiven her. After James dies, Rose visits Sugar Alexandria for the first time in decades. The two women embrace, weep, and spend the night reminiscing. Anna returns the friendship locket she tore from Rose's neck at the hospital. Rose asks that she and James both be buried at Sugar Alexandria, and Anna consents, recognizing that the bond destroyed in life will be reunited in death. After Rose departs, Anna retrieves a small figurine James carved of Rose, its two perfect legs a testament to how he saw past her disability. Forgetting her medication, Anna hears the paintings begin to speak. She puts a finger to her lips and shushes them with a wide grin, her girlish spunk still shining through.