After Thomas's death, Dominick discovers the identity of their birth father, who was part African American and part Native American–a secret their mother had shared with Thomas, but not with him. He succeeds in getting Thomas released, but Thomas soon dies, apparently by suicide. In the course of Thomas's treatment, Dominick is covertly informed of sexual abuse taking place in the hospital, and helps to expose the perpetrators. She helps Dominick come to understand Thomas's illness better and the family's accommodations or reactions to it. Rubina Patel, a psychologist employed by the hospital. First in Thomas's interests, and then for his own sake, he sees a therapist, Dr. Dominick also displays classic symptoms of PTSD, as a result of stressors in his adult life. In the process, Dominick contemplates his own difficult life as Thomas's brother, his marriage to his gorgeous ex-wife, which ended after their only child died of SIDS, and his ongoing hostility toward his stepfather.

Dominick sees him through the ensuing decision not to attempt to reattach the hand, and makes efforts on his behalf to free him from what he knows to be an inadequate and depressing hospital for the dangerously mentally ill. Thinking he is making a sacrificial protest that will stop the Gulf War, Thomas cuts off his own hand while at a public library. With medication, Thomas is able to live his life in relative peace and work at a coffee stand, but occasionally he has severe episodes of his illness. Dominick Birdsey's identical twin, Thomas, suffers from paranoid schizophrenia. The novel takes place in Three Rivers, Connecticut, in the early 1990s. It was featured in Oprah's Book Club for June 1998. I Know This Much Is True is the second novel by Wally Lamb, published in 1998.

I know this much is true lamb