In October, the Quai Voltaire smells of wet stone and fading linden trees, of tobacco and the silt of the Seine, which flows sluggishly and dark green beneath the bridges. I stand before one of the tall white portals, notebook under my arm, and read one last time the address written for me on a small piece of cardboard—in handwriting that brooked no doubt: angular, clear, without a single superfluous flourish.