In May 1961, an elderly woman in Paris heard a knock at the door of her six-story walk-up apartment. It was only the most powerful man in the world. The president of the United States was going door-to-door hoping to find the call girl he had discreetly arranged to meet. John F. Kennedy, it turned out, used a fake excuse about a doctor’s visit to attend a long-arranged dalliance while in Paris for a crucial summit, only to wind up in the wrong building, knocking on the doors of random Parisians who were left with the surprise of their lives....