Plot
Wither describes a future wherein genetic engineering has cured humanity of all diseases and defects. People worldwide have foregone conceiving children naturally in favor of this new science. This generation of perfect humans, later dubbed "The First Generation", have lived very long and prosperous lives. Unfortunately their children, though also born perfectly healthy, were plagued with a virus that killed all females by the age of 20 and all males by the age of 25. Their children's children suffered the same fate. Humanity now scrambles for a cure as society has broken down into large gaps between the rich and the poor. Gatherers hunt for young girls on the streets to sell them into labs for research, and the unwanted ones go into prostitution or are simply killed. Others are occasionally sold to rich men to be their brides.
In Manhattan, Rhine Ellery and her twin brother Rowan live alone in their parents’ old home; their scientist parents were killed in an explosion at their laboratory when the twins were twelve. Now sixteen, Rhine is captured by the Gatherers and sold to 21-year-old Linden Ashby at his estate in Florida. She blames her being chosen rather than killed on her eyes, having blue-brown heterochromia that Rowan shares. Rhine finds herself forced to marry Linden along with two other girls, 18-year-old Jenna and 13-year-old Cecily. They join Rose as Linden's new brides, but the ailing Rose is already 20 years of age and does not have long left to live. Upon meeting Rose, Rhine is told that she and Linden are perfect for each other; they have the same amount of time left. Horrified by this, Rhine instantly begins plotting how to return to Manhattan and her brother.
Life in the Ashby manor is very comfortable. Cecily embraces it, having been an orphan longing for a family, and Jenna endures it forlornly while Rhine constantly thinks of ways to escape. She befriends her servant Gabriel and behaves as a good wife in front of Linden and his father, Housemaster Vaughn, in order to earn the title of "First Wife", which would grant her additional privileges to roam the mansion. Rhine sets that as a goal in order to plan her escape.
Rose grows more ill as Vaughan, an experienced doctor and scientist, experiments with ways to treat the virus and prolong her life despite her desire to die in peace. After her eventual death, Linden isolates himself before Rhine reluctantly coaxes him out of hiding. Soon after, he turns his attention to Cecily, who falls pregnant. Jenna and Rhine bond and Jenna admits that she was a prostitute in the Scarlet District prior to her abduction and was Gathered alongside her two younger sisters, who were shot to death rather than being sold as brides. Rhine offers to help her escape, but Jenna says she has nothing to return to and would rather die in the comfort of Linden’s mansion.
After accidentally going down to the basement with Gabriel, Rhine comes across attendants carting a gurney down the hallway, realizing the body on the gurney belongs to Rose and learning from Gabriel and Deirdre, Rhine’s young domestic, that Vaughan experiments on the bodies of anyone who dies within the mansion. She also learns from Deirdre that Rose had a stillborn daughter when she was nineteen, but that both Rose and Deirdre had heard the baby cry after birth; Rhine comes to believe that Vaughan killed his grandchild to spite Rose and to gain a new test subject.
During a hurricane, the brides, Linden, and Vaughan move to the storm shelter in the basement and Rhine sits with Linden to look over blueprints for houses he’s designed. He has sketched the houses in vivid detail, fascinating Rhine and causing them to bond. They nearly kiss, and Rhine is so disgusted by this that she waits for the next hurricane to break the window in her bedroom. She climbs out and runs across the grounds, becoming seriously wounded by flying debris and being returned to the mansion. She recovers from her wounds and Gabriel expresses his fear of losing her, whereupon they kiss for the first time but quickly separate when they hear a noise in the hallway. Jenna and Cecily come to visit her as her recovery continues and the three sister wives bond further.
Rhine earns Linden’s favor, owing this to her physical resemblance to Rose, and he begins taking her out to events more and more often. She bonds with him, learning that Vaughan has complete control over Linden’s life and that he may be just as much a prisoner as the brides. She has several run-ins with Vaughan in which he warns her not to break Linden’s heart and that she would be a very valuable test subject. He further threatens Jenna, who seems extremely frightened of him, though he seems to think Cecily inconsequential. After weeks of spending time with Gabriel, Gabriel is unexpectedly reassigned to the basement indefinitely. Cecily goes into labor, and though Jenna encourages Rhine to use the opportunity to find Gabriel, Rhine fears leaving Cecily alone with Vaughan when she is so vulnerable. Cecily gives birth to a son that she and Linden name Bowen at Vaughan’s suggestion, neither of them knowing that Linden had a brother who died of the virus years before Linden was born with that same name.
After Jenna sets fire to the sitting room, Rhine sneaks down to the basement and reunites with Gabriel, and the two plan an escape from the mansion. This plan is waylaid by Jenna’s sudden illness, showing all of the signs of the virus despite her being only nineteen at this time. She deteriorates rapidly, far more rapidly than Rose, and each sister wife wonders if this illness is something else entirely. Vaughan’s attempts to treat her fail and she dies early one morning. Cecily’s and Rhine’s grief is extreme, with Rhine refusing to be around Linden until after he takes her to another event. Soon after, she and Cecily meet outside and Cecily confesses that she was the noise in the hall when Rhine and Gabriel first kissed, having told Vaughan and causing his reassignment. She’d also told Vaughan that Jenna had been helping Rhine meet with Gabriel, and Rhine hysterically comes to realize that Cecily’s actions have gotten Jenna killed. She shouts as much at Cecily, who tries to reject this, but Rhine flees back inside the mansion.
Despite the severe snowy conditions, Rhine plots her and Gabriel’s escape a few nights after and leaves without saying goodbye to Cecily, though she gives a cryptic goodbye to Linden. She escapes outside and makes her way through the storm to the gate surrounding the mansion, waiting for Gabriel to arrive. Eventually he does, aided by another attendant, and the two find their way to the docks and board a ship. Gabriel, with his interest in boating, manages to sail them away and Rhine looks forward to the journey and to finding her brother.
