He searched the floor and found two spent cartridges of a heavy calibre automatic.

“They killed the woman, of course,” he said, speaking his thoughts aloud. “I was afraid of this. If I could only have got our men in!”

“You expected him to be murdered?” said Elk in astonishment.

Dick nodded. He was trying the window of the woman’s room. It was unfastened, and led on to a narrow parapet, protected by a low balustrade. From there, access could be had into another room on the same floor, and no attempt had been made by the murderer to conceal the fact that this was the way he had passed. The window was wide open, and there were wet footmarks on the floor. It was a guest room, slightly overcrowded with surplus furniture, which had been put there apparently by the housekeeper instead of in a lumber-room.

The door opened again into the corridor, and faced a narrow flight of stairs leading to the servants’ quarters above. Elk went down on his knees and examined the tread of the carpet carefully.

“Up here, I think,” he said, and ran ahead of his chief.

The third floor consisted entirely of servants’ rooms, and it was some time before Elk could pick up the footprints which led directly to No. 1. He tried the handle: it was locked. Taking a pace backward, he raised his foot and kicked open the door. He found himself in a servant’s bedroom, which was empty. An attic window opened on to the sloping roof of another parapet, and without a second’s hesitation Dick went out, following the course of that very precarious alleyway. Farther along, iron rails protected the walker, and this was evidently one of the ways of escape in case of fire. He followed the “path” across three roofs until he came to a short flight of iron stairs, which reached down to the flat roof of another house, and a guard fire-escape. Guarded it had been, but now the iron gate which barred progress was open, and Dick ran down the narrow stairs into a concrete yard surrounded on three sides by high walls and on the fourth by the back of a house, which was apparently unoccupied, for the blinds were all drawn.

There was a gate in the third wall, and it was ajar. Passing through, he was in a mews. A man was washing a motor-car a dozen paces from where he stood, and they hurried toward him.

“Yes, sir,” said the cleaner, wiping his streaming forehead with the back of his hand, “I saw a man come out of there about five minutes ago. He was a servant—a footman or something—I didn’t recognize him, but he seemed in a hurry.”

“Did he wear a hat?”