Wally Lamb’s I Know This Much Is True centers on the illness of Thomas Birdsey, a middle-aged man who has had schizophrenia for the previous 20 years. Narrated by Thomas’s twin brother, Dominick, the novel opens with Thomas having left the group home where he lives and him cutting off his hand with a knife he took from his stepfather’s weapon collection. Thomas performs this action after reading a Bible verse that commands the reader to “cut off [his] right hand” if it “offends him” (5), interpreting the biblical metaphor literally. It is the fall of 1990, and Thomas believes that the sacrifice of his hand will prevent the US military from escalating its involvement in a conflict in the Persian Gulf.

As Dominick lobbies for Thomas’s release back to a minimum-security facility, he wrestles with his conflicting emotions of anger, frustration, guilt, and regret in regard to several aspects of Thomas’s illness and their relationship. Alternating between the present timeline of 1990 and 1991 and flashbacks to the 1950s and 1960s, the narrative uncovers a history of trauma and family secrets from which Dominick ultimately attempts to heal.

Lamb, the author of six novels, is known for his sweeping family sagas. Both I Know This Much Is True and She’s Come Undone (1992) appeared at #1 on the New York Times Best Sellers list, were New York Times Notable Books of the Year, and were Oprah’s Book Club selections. A television adaptation of I Know This Much Is True was released by HBO Max in 2020. Lamb has also edited a nonfiction anthology of work by inmates from the York, Connecticut Correctional Institute, where he volunteers, as well as a collection of autobiographical essays about his work with the prison. Lamb has received numerous awards and distinctions, including a National Endowment for the Arts grant and the Connecticut Center for the Book’s Lifetime Achievement Award.

This guide refers to the 1998 paperback edition published by Regan Books/Harper Collins.

Content Warning: The source text and this guide discuss mental health conditions, domestic and child abuse, sexual violence and abuse, HIV and AIDS, suicide and suicidal ideation, death of an infant, miscarriage, death, murder, and animal cruelty. This guide quotes offensive language referring to neurodivergent people.

Plot Summary

The novel opens on October 12, 1990, as Thomas Birdsey, a 41-year-old man who has schizophrenia, cuts off one of his hands while seated in a Connecticut public library. The action, he believes, will prevent the escalation of US military involvement in the Persian Gulf. Thomas’s twin brother, Dominick, serves as the novel’s narrator. Despite the surgeon’s advice, Dominick follows Thomas’s wishes in refusing to allow the limb to be reattached. When he is released from the hospital, Dominick accompanies Thomas back to the Three Rivers State Hospital, where Thomas has resided at various junctures. This time, however, Thomas is placed in Hatch—the maximum-security wing of the hospital—for a mandatory stay of at least 15 days. Dominick, knowing that the maximum-security conditions will only speed Thomas’s mental decline, is certain that the placement is a mistake and immediately sets about getting Thomas moved to Settle, the minimum-security unit to which Thomas is accustomed. He learns from Thomas’s new case manager, Lisa Sheffer, and his assigned therapist, Dr. Patel, that the 15-day stay cannot be reversed. Thomas must undergo evaluation and observation by a team that includes Sheffer and Patel; at the end of this period, a hearing with the state’s psychiatry board will be held. The board will consider the team’s recommendation in determining whether Thomas can be returned to a minimum-security facility or should be remitted to Hatch for a one-year minimum stay.

The narrative alternates in time between the aftermath of the incident and key periods in the twins’ past, focusing on the summer of 1969, when Thomas’s illness emerged. Scenes from the Birdseys’ childhood reveal their background: Born to an unmarried woman of Italian descent named Concettina Tempesta on the last day of 1949 (Thomas) and the first day of 1950 (Dominick), the twins grow up in the house built by their grandfather—an immigrant who died just before their birth and whom Concettina revered. When the boys are still under 10, their mother marries Ray Birdsey, who, though he legally adopts the boys, is a strict and abusive father. Thomas’s traits—which Ray deems weak and effeminate—make him an especially vulnerable target for Ray’s abuse.

Dominick also recalls Concettina’s death in 1987 of breast cancer. In the months leading up to her death, Dominick, hoping to provide her with a meaningful gift, hired a PhD student to translate his grandfather’s memoir—handwritten in Italian by the patriarch as he neared the end of his own life and which Concettina, who does not read or speak Italian, has never read. The translation, however, is not finished in time, and the PhD student—Nedra Frank—disappears with the manuscript after an argument with Dominick. Dominick is certain that the manuscript is lost forever.

As he waits for his security clearance to be approved, Dominick visits Hatch daily, keeping up to date on Thomas’s condition via Sheffer and Patel. Patel begins playing Dominick audio recordings of her sessions with Thomas in the hope that Dominick can make sense of some of the things Thomas says. Thomas is certain that he is in a kind of governmental protection facility because he is valuable to the Soviets. He continues to insist that his self-dismemberment, which was inspired by a specific biblical passage, is for the good of the country and that he has been tasked by God with preventing a future war. As they talk, Dominick begins to meet with Patel for his own professional therapy, though he is initially highly resistant. Their conversations reveal Dominick’s anger and frustration at being his brother’s lifelong caretaker, protector, and advocate as well as his fierce loyalty toward him. As the “healthy twin,” he harbors frequent resentment toward Thomas, and as they grew toward adulthood, Dominick longed to break free of the burden that Thomas placed on him. A promise to their mother upon her death to care for Thomas, however, has left Dominick guilt-ridden, feeling that he has let his mother down. Other life trauma—specifically the sudden death of his infant daughter at three weeks of age and his subsequent divorce from his wife, Dessa, have hardened and disillusioned Dominick. The trauma of Dessa’s departure from the marriage resulted in Dominick experiencing anxiety attacks, which led to the end of his career as a high school history teacher. As the novel unfolds, he runs his own painting company and faces daily angry messages from his current customer as the job lags in progress due to his dealings with Thomas’s affairs at Hatch. Dominick lives with his girlfriend, Joy, who is friendly and upbeat, but she is 15 years his junior and frustrated with Dominick for consistently placing Thomas’s needs above her own.

Thomas’s talks with Patel lead him to focus on the summer of 1969—a turning point in both his and Thomas’s lives, as Thomas’s illness was diagnosed amid the backdrop of the US conflict in Vietnam. Dominick and Thomas begin studies at a local university—a venture that Dominick looks forward to as an opportunity to finally break free from his twin. Their mother, however, convinces Dominick to be his brother’s roommate for the first year, pointing out that Thomas is ill equipped in many ways to depend on himself. Thomas nearly fails his entire first year and is placed on academic probation. His behavior grows increasingly strange. This strangeness only increases that summer when the twins, along with Leo Blood—Dominick’s best friend and later brother-in-law and a local teen named Ralph Drinkwater (an economically disadvantaged boy of African American and Wequonnoc descent who is deemed an outsider)—are placed together on a work crew for a summer maintenance job with the city of Three Rivers. Dominick frequently dwells on memories of Ralph from elementary school, when his twin sister, Penny Ann, was raped and murdered. Dominick begins dating Dessa Constantine (whose younger sister, Angie, Leo will later go on to marry). Dessa’s father is a wealthy and prominent owner of a car dealership and does not approve of her dating Dominick. As the summer draws to an end, Thomas’s behavior is increasingly odd and erratic, especially upon learning that Dominick plans to room with Leo that fall. A conversation with Thomas over lunch one day—in which he informs Dominick that their dentist implanted a listening device inside of him because he is a target of the government, which suspects him of being a Soviet agent—proves to Dominick that his concerns about Thomas are warranted.

As the end of the 15-day period draws near, Dominick is granted security clearance and is finally able to meet with Thomas. He asks Ralph, who is employed at Hatch as a custodian, to keep an eye on Thomas and inform Dominick if it seems like he isn’t being treated well. Sheffer coaches Dominick on the testimony he will give to the board as he asks for Thomas’s release from Hatch. She has come to agree with him that Hatch is no place for Thomas, though Patel insists that she herself has not decided how she will vote, knowing that Settle is preparing to close.

The night before the hearing, Dominick finds a positive pregnancy test in his home trash. Because he sought sterilization immediately after the death of his daughter, he knows that the baby cannot be his own. Angered at the thought of Joy engaging in an affair and stressed about Thomas’s well-being, Dominick goes on a drunken joy ride and totals his truck. He wakes up in a hospital the next morning but, equipped with crutches, is determined to get some painting completed before Thomas’s hearing at four o’clock that afternoon. Certain that he can remove the shutters from the home he is working on—that of the Roods’, an eccentric elderly couple—he forces himself up the ladder despite the pain. As Dominick reaches the third floor, however, he comes face-to-face with Henry Rood, who is standing at the window. Henry shoots himself, dying by suicide in front of Dominick. Dominick falls from the ladder and remains unconscious by sedation for three days.

When he awakens, he learns the trial’s outcome: Patel abstained from voting, and Dominick’s absence was viewed negatively by the board. Thomas was sentenced to be remitted to Hatch for one year. Coincidentally, Dominick’s hospital roommate is Nedra Frank’s fiancé; Dominick recovers the manuscript and begins reading the translation. The story reveals his grandfather to be not the noble hero that Concettina revered for all her life but a self-absorbed bully who belittled Concettina and abused her mother. Dominick wrestles with this new image of his grandfather.

Upon his discharge, Dominick sinks into a state of panic and depression—determined to find some way to reverse Thomas’s sentence and at a loss for how he will continue to perform his job. When Ralph warns him of a guard who is abusing patients, Dominick is able to use this information to strongarm officials into securing Thomas’s release from Hatch. A group home that he once resided in will house him temporarily until his new placement is ready for him. Sheffer warns Dominick that freedom will be jarring for Thomas and that he will need to acclimate slowly.

On his first night at the group home, Thomas escapes. His body is later found in the river at the cemetery where he, Dominick, and Dessa frequently walked. Whether his death is an accident or a suicide cannot be determined, though Dominick is convinced that Thomas died of his own free will.

A small memorial service is held, and Dominick is numb; he is twin-less, as he had once wished, but now permanently. At the end of the day, when only Dessa, Leo, and Angie remain at the reception held at Ray’s home, Dominick lashes out at Ray—accusing him of never visiting nor supporting Thomas and revealing many family secrets about the violence that was the norm throughout the brothers’ childhood. Dominick focuses on a specific moment of abuse that Dominick is certain “caused” Thomas’s schizophrenia.

Dominick sinks further into a depression in the weeks that follow, refusing to speak to Ray even though Patel urges him to return Ray’s calls. Finally, Dominick learns that Ray has had surgery when a doctor calls to tell him about the amputation of a part of his leg. Caring for Ray pulls Dominick out of his depression and forces him to return to life. Joy returns briefly to inform Dominick that she is HIV positive. Dominick tests negative. He finally learns from Ray the identity of his father: the brother of Ralph’s father, who was killed in the Korean War.

As the 1990s close, Dominick renews his relationship with Dessa. They remarry and then adopt Joy’s daughter after Joy dies.