In 1969 Calcutta, three-year-old Varsha Gupta, daughter of a wealthy Marwari Hindu industrialist family that practices strict vegetarianism, suddenly refuses her lunch and demands rice and fish. She insists her "real" mother is a woman named Jhorna who lives beside a river. The declaration shocks the household, especially her mother, Dipika. Varsha's pediatrician, Dr. Monty Bose, finds nothing wrong but notices two birthmarks shaped like snakebite puncture wounds on her ribcage. He recommends the family consult his wife, Shoma Bose, a psychologist who has researched children claiming past-life memories.
The story is narrated by Dinanath "Dinu" Datta, Shoma's nephew, a semi-retired antiquarian in Brooklyn. The narrative alternates between 1969 and 2020, when the COVID-19 pandemic traps Dinu far from his aging aunt. As a child, Dinu split his time between his parents' flat and Tavoy, the bungalow where Shoma and Monty lived. Shoma had previously collaborated with Dr. Catherine Booth at the University of Virginia, studying "cases of the reincarnation type," a term for children who recall previous existences. Fieldwork convinced Shoma that some such memories are verifiable.
Shoma interviews Varsha alone. Speaking in a rural Bengali dialect no city child would know, Varsha describes a mud-walled house by a river, a pond where she caught fish, and cooking on steamboats. She correctly predicts what Shoma will eat for lunch, though the meal has not yet been prepared. Shoma concludes that Varsha's inherited memories include a complete haptic system: the apparatus of taste, smell, and touch of her former self.
Dipika, devastated, becomes Shoma's therapy client. She reveals that an Adivasi woman, a member of an Indigenous tribal community, once confronted her family near their mines in Orissa for destroying a site sacred to Manasa Devi, the goddess of snakes. During Dipika's pregnancy, the same woman appeared three times as a waking vision, saying the child would have important work to do. Shoma recognizes these as "announcing dreams," a documented pattern in reincarnation cases. With Varsha refusing food, Dipika agrees to let Shoma feed the child fish outside the house.
Shoma designs a diagnostic test, serving Varsha several fish species in the family's parked car. The child identifies native Bengali fish with expert precision but cannot recognize tilapia, a recently introduced African species, confirming that her sensory memories belong to someone familiar with local fish but not with non-native species. Varsha also describes visions of thousands of dead bodies floating after a catastrophic storm, events she says have not yet happened.
In 2020, Dinu begins recording his memories at the urging of Tipu, a twenty-four-year-old former climate activist with heterochromia, or mismatched eye color, from a cobra bite who works at the Badabon Trust in the Sundarban mangrove forest. Tipu has discovered that Shoma visited the island of Lusibari in 1969 and suspects a connection to her research, but Shoma refuses to explain. Dinu's account introduces Tavoy's other residents: Husna Mondal, the cook, a Muslim Partition refugee, and Dev Thapa, the driver, whose uncanny perceptual abilities are guided by the Shindaw Nat, a guardian spirit from Burmese tradition.
In a second fish test, Varsha identifies three species of catfish that even Monty cannot distinguish. She reveals her former name was Isha Mondal, her parents were Jhorna and Binu, and she lived near the village of Lusibari in the Sundarban. Varsha's father, Abhay Gupta, a former photography student and something of a black sheep in the family, arranges passage on a company motor launch to take Varsha to the island.
During the river voyage, Varsha names every waterway they pass. She recognizes the guide as someone her previous mother wanted her to marry and identifies Shoma's relative Nilima, who runs a women's union on Lusibari, as "Mashima," a maternal-aunt honorific, accusing Nilima of refusing to help when Isha's father was arrested. At the island, Varsha leads the group to the site of her former home, only to find it submerged, swept away by a breach in the embankment.
Shoma interviews Nilima's husband, Nirmal, a schoolteacher, and confirms Isha Mondal's story. Isha's father, Benoy, was a snake-catcher and follower of Manasa Devi. A local gangster coveted his land for prawn cultivation, had Benoy imprisoned and likely killed, then attacked the family when they refused to sell. Jhorna was stabbed to death. A king cobra, believed sent by the goddess, fatally bit Isha near the heart, an act islanders interpreted as mercy to save her from trafficking. Isha's death preceded Varsha's birth by seven months.
A week later, Abhay is killed in a car accident. Varsha never again mentions her past life. Her ayah, or nursemaid, later reveals that on the morning of Abhay's death, Varsha screamed for someone to warn her father not to drive. When Abhay died, Varsha had a seizure, though no one had told her the news. In a final case note dated 1987, Shoma records her suspicion that a young woman in Ahmedabad who has schizophrenia is Varsha. The woman's condition began after the childhood shock of her father's death in a car accident, and she sought electroshock treatment to suppress powerful visions.
In 2020, Shoma has a heart attack and returns resentfully from a near-death experience, claiming she was with Monty and others who had already died. She begins reporting uncanny knowledge of Dinu's life and predicts Super Cyclone Amphan days before any meteorological warning. During their final call, she tells Dinu she is at peace and asks him to let her go. She dies in her sleep as Amphan strikes Calcutta, leaving Tavoy to Dev and her study's contents to Dinu.
After searching Shoma's anonymized files, Dinu matches dates in her 1969 appointment book to identify her mystery patient, Case J, as Varsha Gupta. Tipu traces Varsha to her alias, "Monsoon Abhayaputri": She became a Wall Street day trader who used the Shindaw Nat, through Dev, to pick stock ticker symbols. Varsha tells Dinu she will believe his account only if he recreates Shoma's fish meals and her body remembers the taste.
After months learning Bengali cooking with invasive Asian fish species sourced in Brooklyn, Dinu prepares the decisive meal. Varsha instinctively takes over the cooking, her body remembering what her mind had suppressed. Her memories flood back: Lusibari, the mud house, Dev, Dinu. She agrees to contact Tipu.
Tipu enlists Varsha for an "irruption," a manifestation of otherworldly phenomena designed to block a coal plant on a Sundarban island containing ruins of a Manasa Devi temple. The campaign combines legal challenges, scientific evidence, and the coordinated efforts of a global network of people with heightened perceptual gifts. After extraordinary events, including tigers breaching the corporate security fence, an apparition of a glowing female figure appears above the ruins at dawn, witnessed by tens of thousands. The Calcutta High Court issues a stay order on the power plant.
In the novel's final revelation, Dinu discovers letters at the University of Virginia showing that he himself was a case of the reincarnation type. As a toddler, he had episodes of acting like a wild animal, the real reason he was sent to live at Tavoy. Dev explains that Dinu was once an otter trained by Isha's father to drive fish into nets, kept loyal by love for Isha. When the otter was killed, Isha prayed to Manasa Devi, who reincarnated it as the child of a woman visiting the Sundarban: Dinu's mother. The goddess promised Isha and the otter would be reunited. Varsha appears in Charlottesville, having learned the story from Dev, sits beside Dinu, and tells him they have been together many times before.