Hi! Looking for a story where the main character is advised by a fortune teller to add an initial to his name. This leads a spy agency to investigate him. Which leads the “other side” to step up research on a nuclear shield. Ultimately, war is prevented, at which point you learn that the fortune teller was an alien vowing to make maximum impact with minimal interference. I read this in the 70s—it could be as early as 50s, from my sense of the style. Ring any bells?