MOVE over Da Vinci, here comes Mary Magdalene. In the latest twist to the seemingly endless literary debate over the roots of Christianity, a controversy is looming over a novel by an author who claims to be descended from Jesus Christ. It may sound familiar to readers of Dan Brown’s blockbuster The Da Vinci Code, but Kathleen McGowan, an American who began her career as a journalist in Belfast, has persuaded publishers that her claims that Magdalene married Jesus and bore his children should be taken seriously. “I don’t want people to think I’m claiming to be some elitist figure...