SEATTLE, Washington—Fresh from the keyboard of science-thriller writer Lori Stephens, Alpha, Omega is—like Dan Brown’s The Da Vinci Code—fiction with a forceful message. The story starts with a corpse. A defector from a cult called Omega has bled to death, and the only clue is the book he’s clutching: the Librah Vae-ta, the holy scripture that the Omega founders engineered over a century ago. Dr.…