On New Year’s Day, 1975, a recently divorced, middle-aged man named Archie Jones tries to commit suicide inside a parked car. A local halal butcher discovers Archie and saves his life. Feeling renewed from the thrill of being saved, Archie stumbles upon a house full of young people recovering from a party. One of these people is Clara Bowden, a tall, stunning young Black woman much younger than Archie. Archie and Clara marry just six weeks after they meet.

Clara has immigrated to London from Jamaica with her mother, Hortense Bowden, a devout Jehovah’s Witness. Clara turns away from Hortense’s religion. After Clara marries Archie, Hortense rejects Clara for marrying a white man. Clara is not in love with Archie, but she recognizes him as a good man and appreciates the life he gives her. Archie resumes most of his bachelor routine shortly after his marriage, spending most of his time with his friend Samad Miah Iqbal at O’Connell’s, an Arab-owned bar that is their home away from home.

Archie and Samad’s friendship goes back to World War II when they served in a British Army tank battalion. During that time, Samad and Archie helped capture a Nazi scientist, Dr. Perret, and had the chance to execute him. The two young soldiers argued about who should do the killing. Archie Jones led Dr. Perret off the road. A shot rang out, and Archie returned to Samad’s side. This dark incident created a bond strong enough to withstand almost thirty years of separation after the war. In 1973, when Samad and his new, young wife Alsana emigrate from Bangladesh to London, Samad moves into Archie’s neighborhood. 

The Jones and Iqbal families maintain their friendship for the next 25 years. Alsana Iqbal and Clara Jones become friends, at first just because their husbands spend so much time together but then because they have so much in common as immigrants and wives of older husbands. Alsana and Clara give birth at the same time. Alsana has twin boys, Magid and Millat. Clara has a girl, Irie. The three children play together, go to school together, and compete with each other. 

In 1984, when his twins Magid and Millat are nine years old, Samad becomes infatuated with their music teacher. Because he is a devout Muslim, Samad is tormented with guilt over this relationship. He decides that he is not a good enough Muslim to serve as a role model and vows to send the boys back to Bangladesh for a traditional upbringing. However, Samad can afford to send away only one boy. After much indecision, Samad chooses to part with Magid. Samad makes this decision without consulting his wife, and Alsana responds with years of anger and silence.

By the time Millat, the London twin, enters high school, he has a well-deserved and cultivated reputation as a womanizer and tough guy. Irie Jones is obsessed with Millat from the time she enters puberty. Millat takes Irie for granted as his childhood friend, but she hangs out with him because she hopes for more. One afternoon Irie and Millat get caught smoking after school. As punishment, they are required to get extra tutoring. Their tutors are an aging hippie couple, Joyce and Marcus Chalfen. Marcus Chalfen is a genetic engineer who is creating a new species, FutureMouse, to produce specialized cells at predictable times. The Chalfens take over Irie’s and Millat’s lives. Joyce is so attracted to Millat that she makes him large loans and showers him with gifts. Marcus puts Irie to work as his secretary. 

Samad’s decision to separate his sons has unexpected consequences. Magid, the older son in Bangladesh, becomes pro-British, anti-religious, and interested in science. In London, Millat moves from wanting to be a gangster to becoming a religious terrorist. He joins KEVIN (Keepers of the Eternal and Victorious Islamic Nation), an extremist group that burns anti-Muslim books. Marcus Chalfen acquires a new disciple when Magid starts sending letters to Marcus from Bangladesh. Meanwhile, Joyce and Marcus’s oldest son, Joshua, joins FATE (Fighting Animal Torture and Exploitation), an animal rights group. 

Magid returns from Bangladesh to Britain and becomes Marcus’s assistant in the FutureMouse project. Magid and Millat are completely at odds with each other. Joyce Chalfen and the Iqbals grow concerned over Millat’s increasing involvement with KEVIN. They conclude that the best solution to the problem is to make peace between the twins. Since Irie is the childhood friend of both boys, she gets the task of setting up their meeting. When Irie visits Millat, they have a passionate sexual encounter, but immediately afterward Millat falls to his knees and prays for forgiveness. Irie, deeply hurt, flees to Magid and makes love to him as well. Shortly thereafter Irie learns she is pregnant and realizes she will never know which twin is the father of her child.

Marcus and Magid set up a public demonstration of FutureMouse’s genetic evolution, which will begin on December 31, 1992. KEVIN, FATE, traditional Muslims like Samad, and the Jehovah’s Witnesses all oppose these experiments and converge on the Perret Institute for the debut of FutureMouse. The Iqbal and Jones families also attend. Dr. Marc Perret appears at the head table. Samad Iqbal realizes that Archie Jones lied about shooting Dr. Perret back in May 1945. At that very moment, Archie sees Millat pull out a gun. Archie throws himself between Millat and his target, saving Dr. Perret’s life for the second time. Then Archie crashes into the table and smashes the glass box that holds FutureMouse. The mouse disappears into an air vent.

Millat and Magid both get punished for the attempt at murder because the eyewitnesses cannot tell the twins apart. They are sentenced to community service. In time, Joshua Chalfen and Irie Jones become lovers. The story ends on New Year’s Eve, 1999. Irie sits on a beach in Jamaica with Hortense, her grandmother, Joshua, and her little daughter. On that same night, in London, Archie and Samad play cards with Clara and Alsana, on the first night that O’Connell’s opens its doors to women.