Daniel Isaccson is a graduate student at Columbia University. He is living under the pressure of his parental legacy. His parents were famous liberals, who were tried and convicted by the American Government for espionage. They were both later executed. Throughout the novel, Daniel is trying to come to terms with this.
He writes The Book of Daniel, as his dissertation for school. He thinks that by writing his story, it will help him piece together his history. We see that Daniel is not really living in reality. He struggles with his marriage and we see he has a problem with his temper, and can even be sadistic with his wife. He has a sister, Susan, who is in an institution for trying to commit suicide. We learn, through Daniel's writings, that he and Susan weren't very close. They had lived with an aunt after their parents died, but that didn't work for them. They were then sent to live in a shelter in the Bronx, until they were adopted by Robert and Lise Lewin.
As Daniel looks back at his parents, he can't decide if they were guilty or not. He questions everything.
"In any event, my mother and father, standing in for them, went to their deaths for crimes they did not commit. Or maybe they did commit them. Or maybe my mother and father got away with false passports for crimes they didn't commit. How do you spell comit? Of one thing we are sure. Everything is elusive. God is elusive. Revolutionary morality is elusive. Justice is elusive. Human character. Quarters for the cigarette machine."
We can see by this quote that Daniel is is trying to make sense out of anything. He writes the Book of Daniel, as a way to make sense of things that happened. He is still left with more questions than answers.