Brothers Subhash and Udayan Mitra are growing up in Calcutta in the 1960s. Their neighborhood, Tollygunge, is full of refugees whose lives were displaced by the 1947 Partition of India, but the boys themselves live in a modest, middle-class home which sits on the edge of a stretch of land occupied by two ponds. Between the two ponds there is a lowland, which floods in the rainy season.
The boys are one year apart in age, and inseparable. The older, more reserved Subhash often finds himself roped into trouble by his younger, more impulsive brother Udayan. As the boys enter their collegiate years and attend separate local universities, they begin to drift apart for the first time in their lives. Udayan falls in with a group of radicals associated with the Communist Party of India (Marxist-Leninist)—a splinter group of the Communist Party of India with ties to the burgeoning Naxalite movement, a violent uprising originally started by poor sharecroppers in the West Bengal village of Naxalbari. Amid the violence and unrest, Udayan devotes his days and nights to CPI(ML) activities, while Subhash decides to pursue a Ph.D. in America. Udayan begs Subhash not to leave India, but Subhash feels the distance between himself and his brother is already too wide to bridge.
In America, Subhash attends university in Rhode Island, at which he is one of the only Indian students. His feelings of isolation increase when a letter from Udayan arrives saying he has gone against their parents’ wishes for an arranged marriage and chosen to marry a woman named Gauri for love. Subhash, who had been proud of himself for taking a bold new step in moving to America, feels “defeated by Udayan all over again.” Throughout his second year of graduate school, Subhash fields frequent letters from Udayan asking when Subhash is going to come home and allow their parents to arrange a marriage for him. The letters almost never mention Naxalbari or any radical politics at all, and Subhash is relieved that his brother has settled down. Subhash becomes involved with a young, married white woman named Holly; though he knows the relationship is not tenable in the long-term, he is heartbroken when Holly ends their affair. At the end of summer, a letter arrives from Calcutta, telling Subhash that Udayan has been killed and urging him to come home as soon as he can.
Subhash returns to Calcutta to find it completely changed by the violence of the Naxalites. Subhash realizes that his brother had never given up his radical politics and was likely killed by police. Subhash’s parents are so sidelined by their grief that they barely notice Subhash’s presence, and will not answer any of his questions about Udayan’s death. The only one who holds the answers Subhash seeks is Udayan’s widow, Gauri—who is pregnant with her late husband’s child. Gauri is being isolated by Subhash’s parents in a combination of ritual mourning custom and their desire to edge her out of the house so that they can raise Udayan’s child alone.
Gauri reveals what happened the night of Udayan’s death: she and her mother-in-law came back from holiday shopping to find policemen swarming the house. The policemen held Gauri and her in-laws at gunpoint and directed them to the flooded lowland, where Udayan was hiding. After coaxing him out by threatening to kill members of his family, the police put Udayan into a van and let the rest of the Mitras go. The family retreated into the house and, from their terrace, watched as the police executed Udayan, point-blank, in the middle of the field beyond the lowland. The police took Udayan’s body and never returned it.
Subhash is so perturbed by both the details of his brother’s death and his parents’ cruel mistreatment of Gauri that he is unable to sleep for days. After a group of investigators come to the house to question Gauri about the activities of the local CPI(ML), Subhash realizes that in order to keep Gauri safe, he must marry her himself and take her back to America. Gauri reluctantly agrees, though she warns Subhash that Udayan would never have wanted such an arrangement.
Gauri arrives in Boston, five months pregnant. As she adjusts to life with Subhash, she struggles with feelings of isolation and a desire to pursue her education. She rips up her saris, cuts off her hair, and begins attending philosophy lectures at the college. After the birth of “their” daughter, Bela, Gauri’s feelings of isolation and displacement do not abate. She and Subhash embark on a sexual relationship, but even this release of tension does not allow Gauri to feel any peace. Gauri takes a philosophy class and does so well in it that her teacher recommends she eventually pursue a doctorate. As Gauri becomes more dedicated to her studies, her relationship with the young Bela grows more and more contentious. When she is at last admitted to a doctoral program in Boston, when Bela is in first grade, Subhash becomes resentful of Gauri’s desire to escape their home, their marriage, and now their child.
Subhash’s father dies, and he takes Bela—now twelve—on a six-week trip to Calcutta. Subhash’s mother Bijoli, her mind addled by old age, spends her days caring for a cement post in the lowland that marks the spot where Udayan died. After the trip, Bela and Subhash return to Providence to find that Gauri has left. She has written Subhash a note in Bengali, informing him that she has taken a teaching job in California and is leaving Bela to Subhash.
As Subhash and Bela begin adjusting to life without Gauri, Bela becomes withdrawn and loses weight. When a guidance counselor calls to report that Bela is distracted in school, Subhash begins taking her to see a therapist. As the months go by, and Bela enters eighth grade, she begins making friends and participating in school activities. The summer Bela graduates from high school, Subhash receives a letter telling him that his mother has had a stroke—he returns to India without Bela, and Bijoli dies.
After Subhash returns to Rhode Island, he brings Bela to college in the Midwest. As the years go by, she follows in Subhash’s footsteps by studying environmental sciences. After graduation, however, Bela takes up an itinerant existence, travelling across the country and working on different farms. She returns home only a couple of times a year to visit. Every time Subhash sees Bela, he is surprised by how politically-minded and, in some ways, radical she has become, and worries that Udayan has reclaimed Bela from beyond the grave.
Meanwhile, on the West Coast, Gauri lives an isolated but successful life. She has published three books and has a tenured teaching job at a university in Southern California. She regrets having betrayed Bela but is too grateful for her freedom to dwell much on what she has done to her family. Subhash, now a man of sixty, lives a similarly isolated existence. At the funeral of a friend from graduate school, he meets a woman named Elise Silva—a widow and former high school teacher of Bela’s who now runs the local historical society. She and Subhash begin seeing each other.
Bela is in her early thirties, and living in Brooklyn with a cooperative of artists, nomads, and radicals. She knows that her itinerant life is due to the influence of Gauri’s abandonment, but shows no signs of wanting to live any other way. One June, Bela returns to Rhode Island for a visit, and reveals that she is pregnant. She has no relationship with the child’s father, and instead wants to raise it on her own in Rhode Island, in the house she grew up in. Subhash is moved to tell Bela, at last, the truth of her parentage. Bela reacts poorly, at first, but after a trip to the coast to stay with a friend, she returns home and tells Subhash that knowing the truth does not change the fact that Subhash is her only father. If anything, she says, she loves him more, knowing now all he has done for her.
Back in California, Gauri reluctantly agrees to be interviewed by a former student for a book he is writing on the Naxalite movement. The interview brings up painful memories, and the lingering fear that she will be implicated for her tangential involvement, through Udayan, in the movement. One day, Gauri receives a letter from Subhash, asking her to sign some papers finalizing a divorce between them. Rattled, Gauri retreats into her memories of the early 1970s. Back then, she helped Udayan deliver letters on behalf of the CPI(ML) and was instrumental in the killing of a prominent policeman—Gauri tracked the man’s schedule and reported back to Udayan the times when he was off-duty and unarmed so that Udayan’s group could murder him. To this day, Gauri is haunted by the things she did.
A few weeks after receiving Subhash’s letter, unable to compose a sufficient written response, she decides to stop in Providence on the way to a conference in London, to hand Subhash the papers in person and apologize for her actions. When Gauri rings the doorbell of her old house, however, it is Bela who answers. Subhash is not home, and so Gauri sits with Bela and her four-year-old daughter, Meghna, attempting to make small-talk and find out the details of their lives. Bela is enraged by her mother’s presence and refuses to answer any of her questions. She berates Gauri for leaving, telling her that she is “nothing.” Gauri leaves and flies to Calcutta instead of London, determined to confront her past. She visits the lowland, which has been filled in and built up—condominiums now stand on the site of Udayan’s execution. Gauri considers committing suicide by throwing herself off the balcony of her room in a local guesthouse, but ultimately loses her will to die, and returns to California.
Subhash and Elise, now married, go on a honeymoon to Ireland. Visiting a circle of stones in the countryside, and seeing the flooding all around them, Subhash is reminded of the lowland. The narrative flashes back to the evening of Udayan’s death, revisiting his last moments from his own perspective. Udayan struggles to hide from the police underwater in the flooded lowland but cannot hold his breath long enough. He worries, in his final moments underwater, that his dedication to the revolution has helped no one, and instead had sown only violence and discord. As the police march Udayan across the field beyond the lowland, he knows he will die. He recalls meeting Gauri for a date one afternoon in front of a movie theater, and as the police’s bullets rip through him, his last thoughts are of the sunlight on her hair.