"Only we've got the law on our side and they haven't," he thought; and as the thought ran through his brain he felt the blood pulsate sharply and there was a heavy throb at his heart, for there was a peculiar sound away to his right, high up the steep slope of the cliff, as if a stone had been dislodged and had slipped down a few yards before stopping in a cleft. He stood listening intently, but the sound was not repeated--all was still as death; but the man's pulses had been stirred, and his heart beat in a manner that was painful. It was not that he was particularly wanting in courage, but, shut in there by the darkness, it was impossible to keep back the thought that a desperate man who had stolen out or hidden might be lurking close by ready to spring upon him in an unguarded moment, drive him off the cliff shelf which formed his beat, and all would be over in an instant. For a fall there meant death by drowning or the fearful crash on to the rocks below. "They shan't take me unawares," he thought, and then he hesitated as to whether he should give the alarm by firing his piece. In an instant he had raised it and his finger was on the trigger, but he did not make its flash cut the darkness for a moment and its report run re-echoing along the cliffs. "What for?" he said to himself; "bring the fellows here to laugh at me because I heard a rabbit on the move. I should never hear the last of it." He again grounded his piece, but very softly, and stood with his back to the sea, straining his eyes in the direction from whence the sound had come, but the stones that towered up were all blurred together into one black mass, and though he fancied several times over that he could make out the figure of a man half-hidden by some projection, he was fain to confess directly after that it was all fancy. "But fancy or not," he said to himself, "I don't mean to be taken on the grand hop,"--and he did not stir from his position where he stood on the very edge of the cliff shelf, but kept on glancing to right and left along the stone path, and sweeping the slope in front. Ten minutes passed like this--ten long-drawn intervals of time--and then the man threw up his rifle and stood ready, fully expecting an attack, certain now that there had been good reason for the dislodgement of the stone. For from high up on the top of one of the ranges of prison buildings a sound rang out which sent a thrill through the watcher's nerves. It was the alarm bell, which might mean the escape of prisoners or an attack from a deadly enemy; but it could not be the latter, for there was no reflection of a fire. "Now for it!" muttered the man, with his finger on the trigger, prepared for the rush of a man or men, and he thought over the formula he must utter before he fired.