The book opens in a Nazi concentration camp where Simon is working along with his friends Arthur, Josek, and Adam. The conditions are extremely difficult: they have little food and are forced to do hard labor for the Nazis. The SS officers brutalize them, and if they refuse to work or cannot work, they are shot. Simon feels that he is no longer treated like a human being.
Arthur and Josek often have disagreements, because Josek remains steadfast in his faith in God, while Arthur and Simon question what kind of God could allow the atrocities occurring around them. Simon finds truth in one woman’s bitter joke that God is on leave.
That morning, Simon is separated from his friends and selected to work in a makeshift hospital which has been set up in the Technical School where Simon studied architecture. As they travel, Simon notices a military cemetery, where a sunflower lies on each grave. Simon envies the dead soldiers, because he thinks he will be buried without this distinction of humanity and remembrance.
When Simon arrives at the school, he remembers how even before the war, anti-Semitism had been rampant. The students had devised a “day without Jews” during exams, in which Jewish students were brutalized and the police could do nothing because the school was outside their jurisdiction.
Just before Simon is assigned duties at the hospital, a nurse asks him if he is a Jew. She brings him to the bedside of a dying Nazi soldier named Karl, who is bandaged from head to toe. Karl tells him that he must confess a terrible crime he has committed, and begins to explain his life story: he was born in Stuttgart and joined the Hitler Youth over his parents’ objections. He then volunteered for the SS. As Karl tells his story, Simon picks up a letter that had fallen, holds Karl’s hand, and shoos a fly away from Karl.
Karl then admits his crime: about three hundred Jews had been forced into a house that was then set on fire. When a mother, father, and small boy tried to jump from the burning house, Karl and other Nazis shot them. He is haunted by their image and begins to weep.
Simon is disgusted by his story, and at several points he tries to leave, but Karl objects. At the detail about the young boy, Simon remembers a young child from the Lemberg Ghetto named Eli. Eli had miraculously survived many of the raids on young children, including an incident in which a fake kindergarten was set up in order to lure parents to send their children to it. When they did, the children were promptly taken to the gas chambers. Eli had stayed home that day. He is the last Jewish child that Simon had seen.
Karl continues his story: he fought in Crimea, until one day, climbing out of the trenches, he was stopped in his tracks by the memory of the Jewish family, and just then a shell exploded near him. Karl’s face and body had been torn to ribbons, and the pain was unbearable. Karl then asks Simon to forgive him for the crimes he has committed so that he can die in peace. Simon does not say anything, and then walks out of the room.
Simon rejoins his friends in the camp, and explains what happened with Karl. Arthur and Adam are happy to hear there is one less Nazi in the world, and Josek is glad that Simon did not forgive Karl, saying that Simon could not forgive crimes on behalf of other people. That night, Simon is haunted by the image of Eli in a bloody heap. Simon wakes up screaming.
The next day, Simon returns to the hospital. The nurse tells him that Karl died in the night and left Simon his possessions, along with a name and address for his mother. Simon refuses to take the bundle. He tells his friends, who have become disinterested in the story.
The next two years are filled with death and hunger. All three of Simon’s friends die in the camps. One night, the memory of Karl haunts Simon, and he explains his situation again to a fellow prisoner named Bolek, who is Catholic. Bolek argues that Simon should have forgiven Karl because Karl had no one else to ask.
Simon is liberated from the Mauthausen camp in 1945, and one afternoon is reminded of Karl by a sunflower. He remembers Karl’s mother’s name and address, and goes to visit her. She tells him about Karl, confirming Karl’s own story about his childhood. Simon does not reveal the truth about his experience with Karl. By remaining silent, he does not rob Karl’s mother of her positive memory of her son.
Simon then asks the readers what they would have done in his place. The second section of the book, entitled “The Symposium,” consists of fifty-three responses to his question. They include responses from a cardinal, several rabbis, the Dalai Lama, Desmond Tutu, and Albert Speer to name a few.
The respondents draw mostly on their religious upbringing to answer Simon’s question, and some patterns emerge in the responses. Those who argue against forgiving (most of whom are Jewish) reason that Simon cannot forgive crimes in the name of others, and that murder is unforgiveable for this reason. Some believe that repentance alone does not justify forgiveness, and that Karl demonstrated his anti-Semitism by asking a random Jew for forgiveness, as if all Jews are an undifferentiated mass rather than a diverse group composed of individuals.
Those who argue in favor of forgiving (most of whom are Christian) argue that there is no limit to forgiveness. They argue that if Karl was sincerely repentant, as Simon states that he was, he should be forgiven for his crimes because this would not preclude judgment by God, or they argue that Simon should forgive because forgiveness is divine. Others argue a different angle: that forgiveness would free Simon from his own inner turmoil.
Yet, most of the respondents agree on two ideas: first, that even if these crimes are forgiven, they should never be forgotten; and second, that even if Simon did not explicitly forgive Karl, he acted with an immense amount of compassion given his circumstances.