One night, when Kenneth was returning alone to his billet, he heard the thin squeak of a bat, and glanced up, though it was so dark that he could scarcely expect to see the animal. To his surprise, he caught a momentary glimpse of it as it flew across the lane. It was as though a moonbeam had flashed upon the wings for the fraction of a second. But the moon was not up. The sky was clouded; only one or two stars were visible; and the rays of a star were too feeble to light up the flittering wings. Kenneth was puzzled. He stood still, looking up, waiting for the bat to reappear. It was circling somewhere above him; he could still hear it faintly squeaking; but it did not again come within view, and after a while the sound ceased. "Extraordinary!" thought Kenneth. He was about to move on when he heard the grating of a key in a lock, so slight that it might have passed unnoticed had he not been listening intently for the bat. In this quiet lane, with trees on one side and a garden wall on the other, the sound challenged curiosity. The villagers were forbidden to leave their cottages after dark; Kenneth himself had only chosen this route as a short cut to his billet; he could not help suspecting that one of the inhabitants was breaking rules and entering his house by a back way to avoid detection. It was no part of his duty to play the policeman, and he would have gone on his way if he had not at this moment heard a light, hasty footfall, as of one walking quickly but cautiously. Instinctively he remained still, keeping close to a tree trunk. A man passed him, moving very quietly, almost touching him. He appeared to be in uniform. A second later he heard the key again. Then all was silent. He was now interested, suspicious. The man was going in the direction from which he had come. Who was he? What was he doing at this late hour? For a moment he thought of following him; but he was averse to getting a man into trouble for what was perhaps a harmless escapade, and he decided to proceed. A few steps brought him to a door in the wall. The man must have been silently let out, and must have left without a word, the door being then as quietly closed and locked behind him. The wall, as Kenneth knew, bounded the gardens of two or three of the larger houses. It might perhaps be worth while to find out from which house this nocturnal visitor had departed so stealthily. It was too dark to see; Last Post would be sounded in a few minutes; all that he could do was to put a mark upon the door which he could identify next day. He scratched a cross with his pocket-knife on the right side of the door, on a level with the keyhole, which was on the left, and went on, treading lightly by instinct.