It was a fine morning in late spring. He was wearing an open shirt and a short jacket. His baggy trousers were held up with a broad leather belt; his worker’s boots scuffed the powdery dirt in the street. He had only two and a half miles to walk.

The geography of Paris was very simple. Beginning with the ancient oval of settlement on the banks of the Seine around its central island, the city had gradually expanded down the centuries, enclosed by walls that were built in a series of ever-larger concentric ovals. By the late eighteenth century, just before the French Revolution, the city was enclosed by a customs wall, approximately two miles out from the Seine, at whose many gates there were toll booths controlled by hated tax collectors. Outside this large oval lay a huge ring of suburbs and villages, including, to the east, the cemetery of Père Lachaise, and to the north, the hill of Montmartre. Since the Revolution, the hated old customs wall had been dismantled, and just before the recent war with the Germans, a vast line of outer fortifications had enclosed even the outer suburbs. But many of them, especially Montmartre, still looked like the ancient villages they were.

At the bottom of the hill of Montmartre, Thomas crossed the untidy old Place de Clichy, and entered a long boulevard that ran southwest, along the line of the dismantled customs wall, with the streets of the city on his left, and the sprawling suburb of Batignolles village on his right. Occasionally a tram pulled by a team of horses rumbled slowly past him, but like most laboring men he seldom cared to pay the fare to go on the trams and omnibuses whose horses, in any case, hardly went faster than a brisk walk.

After half an hour, he came to a line of smart iron railings on his left, through which one could see the green spaces of the Parc Monceau. Formerly a princely garden, now an elegant public space, the Parc Monceau was the entrance to an exclusive quarter. Gathered around its southern side were the impressive private mansions of the richest bourgeoisie. But its most charming feature lay up here, in the middle of the railings on the northern side.

It looked like a small, round Roman temple. In fact, it was the old toll booth. But in keeping with its aristocratic surroundings, this humdrum function had been served by a perfect, domed rotunda encircled by classical columns. Thomas liked the little temple. It was also the sign that he had reached his destination.

Crossing the boulevard, he walked northward fifty yards and turned left into the rue de Chazelles.