Surgeon-Major Thomson had apparently forgotten his appointment to view camp bedsteads, for, a few minutes after he had left Geraldine and her brother, his taxicab set him down before a sombre-looking house in Adelphi Terrace.

He passed through the open doorway, up two flights of stairs, drew a key of somewhat peculiar shape from his pocket and opened a door in front of him.

He found himself in a very small hall, from which there was no egress save through yet another door, through which he passed and stepped into a large but singularly bare-looking apartment.

Three great safes were ranged along one side of the wall, piles of newspapers and maps were strewn all over a long table, and a huge Ordnance map of the French and Belgian Frontiers stood upon an easel.

The only occupant of the apartment was a man who was sitting before a typewriter in front of the window.