A popular U.S Senator running for President is shot at a rally and a college dropout named Daniel Allen (who calls himself Carter Allen Cash) is arrested for murder. Daniel's father, a successful and respected rheumatologist named Dr. Paul Allen, believes his son is innocent and develops a compulsion to prove that fact. Underlying Paul's obsession, in part, are feelings of guilt. He and Daniel's mother divorced many years ago and little Daniel had to fly back and forth across the country for infrequent visits with Paul and his new family. Could this have damaged the boy?
The story jumps back and forth between Daniel's memories of his past - including parts of his childhood and what he's been up to during the last couple of years - and Paul's activities. Paul acquires a library worth of information about mass murderers and would-be presidential assassins, looking for clues to the mind-set of these individuals. He also hires a private detective, who helps him find out where Daniel has been recently, who he's met, and so on.
Daniel pleads guilty but even this doesn't persuade Paul of his son's guilt. Paul's obsession gets to the point where he neglects (and lies to) his new wife and family to work on Daniel's case.
I found the book engaging with a well-constructed plot. The main characters are three-dimensional and the reader can (mostly) believe they'd behave in the fashion described. The story is rather disturbing but I'd recommend the book.