It is the first day of January, 2021. The world has been stricken by a mass infertility crisis, now in its twenty-fifth year. Oxford historian Theodore Faron , cousin to Xan Lyppiatt , the dictator and Warden of England, describes the confusion, pain, and chaos the world has endured within the pages of his new diary . Humanity has been “demoralized” and “humiliat[ed]” not only by its inability to breed, but by its inability to find a cause or a cure for the infertility crisis. The last child was born in 1995, now known as Year Omega, and the world is “without hope” that another woman will ever become pregnant — the people of the world have sunken into a universal malaise, and a new political order has emerged. The Omegas — the children born in the year 1995 — are a “god”-like, uniformly “beautiful” and “cruel” class of human known to form gangs, paint their faces, and terrorize anyone not of their generation. The State Security Police keeps the authoritarian state’s wishes in order, sending convicts to a mysterious penal colony on the Isle of Man. Theo, who has retained his post as a teacher at Oxford, finds himself up against students unable to see the point of studying history, the “least rewarding discipline for a dying species.” Theo reflects on his past — first on his relationship with Xan, who has assumed control over Britain with the help of a small, sycophantic Council. Once, Theo served as Xan’s adviser. Journalists reported during this time that the two were “close as brothers,” but Theo claims that even during their shared summers at Xan’s family’s estate, Woolcombe , the two were never so close. Theo then recalls his own father’s early death from stomach cancer, which was largely kept from Theo even as his father went in and out of the hospital and steadily declined. At his father’s funeral, relatives told Theo he was the “man of the family now,” but Theo, then and now, has never wanted “anyone to look to [him] for protection, for happiness, [or] for love.” Theo was for years plagued by a recurring nightmare in which his father stood at the foot of Theo’s bed, pointing at him with the bloody, oozing stump of his arm. The dream began recurring after Theo “killed Natalie ,” but now his father “never comes.” Theo recounts the death of his daughter Natalie, whom he accidentally ran over with his car while backing out of the driveway when she was only fifteen months old. The horrific incident drove a wedge between Theo and his wife Helena from which they were never able to recover. She has recently left him for a younger man named Rupert Clavering .
Theo attends services at a nearby chapel, where there is a new woman present — Theo recognizes her as an old student. After services, the woman approaches him, and Theo notices that one of her hands is deformed — he notes that this “save[s]” her from the twice-yearly examinations to which all healthy young women are subjected. The two re-introduce themselves, and the woman — whose name is Julian — tells Theo that she has approached him because she and “a small group of friends” want to stop the many wrongs which are occurring in Britain. Her “group” knows that Theo is the Warden’s cousin, and hopes to recruit him to bring their grievances before the Council. Theo agrees to meet with her group.
Theo visits his old mentor, Jasper Palmer-Smith . Jasper, since Year Omega, has removed himself to the countryside and built a store of food, firewood, and medicine. When Theo arrives at Jasper’s home, he is shocked by how rapidly Jasper seems to be aging. Hilda , Jasper’s wife, is even more senile and disheveled. Jasper asks Theo if he can come live with Theo in Oxford — Jasper has begun to feel “isolated” in the countryside. Hilda, Jasper says, has been considering taking part in a Quietus — a mass ritual suicide of the elderly by drowning.
Theo meets with Julian’s group at a nearby church and is introduced to Rolf , the group’s leader, and Julian’s husband; Miriam , a former midwife; Luke , a priest; and Gascoigne , a lorry driver. The group tells Theo that they have not yet taken any action, but have a list of grievances with the state. They want to call for a general election, stop the government run semen-testing program as well as the compulsory gynecological examinations, end the Quietus, and bestow civil rights upon the Sojourners (foreign immigrants treated as indentured servants). Theo confesses that he has “no influence” with the Warden of England and never has. Julian urges Miriam to tell Theo the story of her brother, and she does. After pushing an Omega woman to the ground while stealing her handbag, Miriam’s brother was sent to the Isle of Man Penal Colony and subjected to horrific treatment. He escaped to Miriam’s house, but after just a few hours the State Security Police tracked him down, took him away, and sent Miriam his ashes. Theo tells the group that there is a lot of mistreatment the country is willing to tolerate “as the price of sound government,” and that the group’s goal of changing “human hearts and minds” has no chance of coming to fruition. Rolf accuses Theo of having met with them despite knowing he’ll never go to the Council; Theo retorts that before he gives the group a final decision, he wants to see a Quietus. Julian tells him that one will be held nearby in three days. Theo says that he will leave a message for the group after he’s witnessed it.
Theo attends the Quietus, where he witnesses old women in white robes preparing to leap into the sea. Among them is Hilda, who has been included in the Quietus apparently against her will. Theo attempts to rescue her, but a soldier supervising the event strikes Hilda on the head, and she crumples into the water. Theo himself falls into the surf, and is near-drowning when a wave flings him back to shore. Back in Oxford, Theo leaves a note tucked into a wall of the church for Julian’s group to find. The note consists of just a single word: YES. He notes, though, that his decision to go see Xan is motivated less by the “horror” of the Quietus itself than his own “humiliation” at having been unable to rescue Hilda.
A driver named Hedges arrives to ferry Theo to London to meet with Xan. On the way into the city, the two see a group of zealots self-flagellating in a park. When Theo asks Hedges whether he believes in God, Hedges tells Theo that he believes mass infertility was God’s “final intervention” in the “mess” of humanity. At Xan’s offices, Theo finds himself before the full Council. Xan wears the opulent Coronation Ring on his hand, and Theo regards it with disdain. Theo expresses his disappointment at not having secured a private meeting with Xan, but Xan insists that the meeting is one of old friends after three years apart. Theo describes the “murder[ous]” Quietus he witnessed, then questions the Council about the Man Penal Colony, the Sojourners, and the compulsory testing of men and women, asking Xan to “do away” with the “degrading” policies “with one signature.” Xan tells Theo that his “concern would have more weight if [he] were [still] sitting” with the Council, and dismisses him brusquely. When Theo returns to the car driven by Hedges, Xan emerges from the building and offers to join Theo for a walk in the park. Xan asks Theo whether he’s been pressured by someone else to appear before the Council, claiming that Theo could never have thought those issues through himself. Theo claims that he lives in the “real world” and hears the complaints of strangers each day. Xan implores Theo to “tell [his] friends to be sensible.” Xan is “not a tyrant, but [he] can’t afford to be merciful.”
Back in Oxford, Theo meets Julian — who also goes by Jules — at a museum. He tells her that Xan knew “someone” had prompted his visit to London. Theo tells Jules not to “waste [her] life on a futile cause.” He also warns her to stay away from Rolf, who is “dragging [her] into danger to satisfy his own ambitions.” Jules tells Theo she must stay with the group because it is God’s will. She thanks Theo for his efforts and the two part ways. Two weeks later, a pamphlet appears on Theo’s doorstep, outlining Julian’s group’s list of demands from the state. The piece of paper is signed “The Five Fishes.” Theo rips the paper into several pieces and flushes them down the toilet, though he wishes for a brief moment “that he could share the passion and the folly” The Five Fishes have. Two members of the State Security Police (SSP) visit Theo. The Chief Inspector George Rawlings and his companion, Sergeant Oliver Cathcart, who is an Omega, question Theo as to whether he knows anything about the “activities of certain people.” Bombs have gone off at two recent Quietuses, and the pamphlets have not gone without notice. Theo tells the police that, as the Warden’s cousin, he will report directly to the Warden with any threats or news of sedition. Once the men leave, he considers warning the Fishes, but has no way of contacting them and would be afraid to be surveilled even if there was—there is nothing for him to do, he decides, but wait. Theo runs into Julian at a market, and tells her that he had a visit from the SSP. He implores Julian to stop her involvement with the Fishes. He tells her that if she ever needs him, she should send for him at St. John Street. As soon as they part ways, though, Theo decides to “escape” on a journey around Europe in an attempt to put the events of recent weeks behind him.
Theo returns to Oxford a few months later after a trip which only “deepened his sense of impending disaster.” A week after his return, while preparing dinner, there comes a knock at the door—it is Miriam. She informs Theo that Julian has finally sent for him—the police have Gascoigne, and the group is going on the run. Theo grabs his coat and diary while Miriam fills a bag of food, and the two hurry to Theo’s car. Miriam tells Theo that Julian is pregnant. Though Theo doesn’t believe her, he drives her onward to the group’s “fall-back meeting place.” The Fishes are gathered there, and Julian approaches Theo to show him her swollen belly. Theo tells the Fishes that they should inform the Warden of Julian’s pregnancy and ensure her safety that way, rather than by going on the run. Julian believes she and her child will die if the Warden has anything to do with its birth. Theo agrees to join the group on the lam, though he and Rolf trade insults. Rolf tells Theo that he is gutless, and has only been summoned because his relationship to Xan is “useful.” Miriam implores the two to stop arguing. Theo suggests the group travel to Jasper’s — he plans to let Jasper use of his home in exchange for the group using Jasper’s. Once there, Theo finds Jasper’s home unlocked; inside, Jasper’s dead body sits in an armchair covered in blood and feces. He has taken his own life. Theo knows that their group cannot stay, so he takes Jasper’s revolver, empties it of its one remaining bullet and places the bullet in his pocket while Miriam gathers supplies. They then exchange Theo’s car for Jasper’s and get back on the road.
The group stops so that Miriam and Luke can take Julian to relieve herself. Rolf tells Theo that once Julian’s child is born, he believes the child will be hailed as the “new Adam” and given absolute power. If that happens, he wants to take Theo on as his adviser. Theo tells Rolf that once Xan sees him as a threat, the government will extract what they need from him — his sperm — and dispose of him. A tire blows, and the group is forced to wait by the side of the road until first light. The group spends the following day resting while Rolf repairs the car, and Theo writes in his diary that he feels “happy” and “at peace” in the company of The Five Fishes and that that he “no longer [has] need of” his diary, as he is no longer the “self-regarding, sardonic, solitary man” who composed the majority of its entries. Back on the road, the group encounters a fallen tree trunk and is forced to stop — Theo realizes it is a trap just as a group of feral, paint-faced Omegas descend on them. While the Omegas dance around the car and begin to break into it, the group plans to join their death dance as a “cover” while Julian runs away. The plan seems to be working, until one Omega makes a move for Julian — Luke cries out for the Omegas to take him instead, and they do. While they rip him apart, the rest of the group takes cover. Once the Omegas leave, their ritual killing complete, Julian insists on retrieving Luke’s body and burying him. Noticing Julian’s tenderness toward Luke, Theo asks Miriam “whose child” she is carrying; Julian admits that the child is Luke’s. Rolf, enraged, steps away from the group, and while Julian hovers over Luke’s corpse, Miriam tells Theo that Julian has begun to fall in love with him, and that Luke, like Julian, was exempt from government testing due to childhood epilepsy. Rolf rejoins the group. At daybreak, Luke’s burial commences, though Rolf makes no move to help Theo, Miriam, and Julian with the rite. Afterward, the four of them lie down together to rest. When they awake in the early evening, they realize that Rolf has abandoned them and taken the car. Theo knows that Rolf will make his way to London, inform Xan of Julian’s pregnancy, and that Xan will then track their group down. Theo plans to go into the nearest village at dark and steal a car, water, and supplies. At nightfall he walks two hours to the nearest village, and selects a house through whose windows he can see an elderly couple watching television. He threatens them with the stolen revolver, and ties them up on them on their bed. They beg for water and visits to the bathroom, and Theo, feeling guilty, obliges them. They tell him that their cleaning woman will arrive in the morning, and Theo tells them that he will leave their television turned up so no one hears them if they scream before then. Theo takes some “disappointing” spoils from their kitchen, then steals their car and, as he drives back for Miriam and Julian, indulges a fantasy in which they find an idyllic deserted cottage and take refuge there for as long as they need to.
When Theo finds Miriam and Julian, Miriam tells him that Julian’s labor has started and that they must find shelter quickly. Theo, without the help of maps, drives through the night to the edge of Wychwood Forest, a place where Theo used to take walks and where, he remembers, there is an abandoned woodshed. The three of them prepare to dump the car in a lake, but hear a radio announcement describing a “group of dissidents” led by “Theodore Faron of Oxford.” As they approach the cottage they hear helicopters overhead, but make it to the woodshed before being spotted. Miriam prepares a makeshift bed for Julian, and Theo builds a fire. Soon, Julian delivers a baby boy, and “the joy is almost too much for [Theo] to bear.” In his excitement, Theo spills a kettle full of water, and Miriam goes out to get supplies, despite the danger of being seen.
After an hour, Miriam still hasn’t returned, and Julian implores Theo to go find her. Though he wants for the two of them to be together when Xan inevitably arrives, Julian insists. Theo makes his way to a nearby house, and inside finds Miriam’s body, strangled to death. He takes her corpse out of the house and lays it beneath a tree, swearing to avenge her. He returns to the shed; together he and Julian mourn Miriam. Theo feeds Julian, and she worries that the two of them will be separated when Xan arrives; Theo promises her that nothing will pull them apart. Soon, Xan arrives. Theo replaces the last remaining bullet into Jasper’s revolver and goes outside to meet him. Theo confirms that Julian is pregnant, but does not reveal she’s already birthed the child. Xan says that he “doesn’t want to frighten” Julian and has brought “everything she needs.” Theo presses Xan to reveal what he plans to do. Xan tells Theo that if Julian’s child is a boy, that child will be the “father of a new race,” and may even be able to “breed again [with Julian] herself.” Xan announces his intention to marry Julian and ensure she’s looked after, then urges Theo to go inside and convince Julian to go with him. When Theo hesitates, Xan takes aim with his gun and shoots. He misses, but Theo returns fire and shoots Xan through the heart. Theo takes the ring from Xan’s corpse’s finger, and the Council members emerge from the woods. Theo tells them that the child has been born, and brings them into the shed to see Julian and her son. While the Council fawns over the child, Theo laments that a new cycle of life has begun “with jealousy, violence, and murder.” He plans to take Xan’s place “for a time;” there are “evils to be remedied.” Julian questions why Theo has donned the Coronation Ring, and Theo is momentarily irritated, but assures her he will take it off “in time.” Theo reaches out and makes the sign of the cross on Julian’s child’s forehead.