At last, a new Dan Brown novel is coming.Six years after the release of his mega-selling "The Da Vinci Code," the Knopf Doubleday Publishing Group announced that Brown's "The Lost Symbol," a thriller set during a 12-hour period and featuring "Da Vinci Code" symbolist Robert Langdon, will come out in September."This novel has been a strange and wonderful journey," Brown said in a statement issued Monday by his publisher. "Weaving five years of research into the story's twelve-hour time frame was an exhilarating challenge.