Yesterday's Son is a science fiction novel by American writer A. C. Crispin set in the fictional Star Trek Universe. It describes the events surrounding Spock's discovery that he has a son. Yesterday's Son and its sequel, Time for Yesterday, make up A. C. Crispin's "Yesterday Saga". The book was the first Star Trek novel other than the movie novelizations to make the New York Times Bestseller List. Source: Wikipedia (en)