On the tenth of March 1938, the night train from Budapest pulled into the Gare du Nord a little after four in the morning. There were storms in the Ruhr Valley and down through Picardy and the sides of the wagon-lits glistened with rain. In the station at Vienna, a brick had been thrown at the window of a first-class compartment, leaving a frosted star in the glass. And later that day there'd been difficulties at the frontiers for some of the passengers, so in the end the train was late getting into Paris.

Nicholas Morath, traveling on a Hungarian diplomatic passport, hurried down the platform and headed for the taxi rank outside the station. The first driver in line watched him for a moment, then briskly folded his Paris-Midi and sat up straight behind the wheel. Morath tossed his bag on the floor in the back and climbed in after it. "L'avenue Bourdonnais," he said. "Number eight."

Foreign, the driver thought. Aristocrat. He started his cab and sped along the quai toward the Seventh Arrondissement. Morath cranked the window down and let the sharp city air blow in his face.

8, avenue de la Bourdonnais. A cold, haut bourgeois fortress of biscuit-colored stone block, flanked by the legations of small countries. Clearly, the people who lived there were people who could live anywhere, which was why they lived there. Morath opened the gate with a big key, walked across the courtyard, used a second key for the building entry. "Bonsoir, Séléne," he said. The black Belgian shepherd belonged to the concierge and guarded the door at night. A shadow in the darkness, she came to his hand for a pat, then sighed as she stretched back out on the tile. Séléne, he t...