That train of thought set him to listening more acutely than before.  Yet, as no more calls reached his ears the attention of the young engineer soon began to flag.

The monotonous lapping of the waves against the stone wall, the constant splashing of water over the rocks and the steady blowing of the wind all tended to make the watcher feel drowsy.

“What on earth can be keeping good old Tom?” Harry wondered, more than once.

It would have been well, indeed, had Harry kept his eyes turned oftener toward the shore end of the wall.  In that case he might more speedily have detected the wriggling, snake-like movement of the big negro moving toward him.

With great caution the huge prowler came onward, raising his head a few inches every now and then and listening.  The black man’s nostrils moved feverishly.  He was using them, as a dog would have done, to scent any signs of alarm on the part of the human quarry that he was after.

At last Harry Hazelton turned sharply, for his own ears were attuned to the stillnesses of the western forests and his hearing was unusually acute.  He had just heard a sound on the wall, not far away.  Instantly the young engineer was on the alert.

Then his eyes, piercing the darkness, made out the crawling, dark form, which did not appear to be more than fifty feet away from him.

For a second or two Harry stared.  But he knew there could be no snake as broad as this crawling figure appeared to be.

“Who’s there?” Hazelton called quickly.

The writhing mass became still, flattening itself against the bed of rock.  Hazelton was not to be deceived, however.

“Who’s there?” Harry repeated.  “You had better talk up, my man!”

Still no sound.  Harry started forward to investigate.  His foot touched against a good sized fragment of rock left there by one of the masons.

Without delay Harry reached down, picking up the rock, which was rather more than half as large as his head.

Holding this in his right hand Harry advanced with still more confidence, for he felt himself to be armed.  Hazelton had been a clever pitcher in his high school days and knew that he could make this fragment of rock land pretty close to where he wanted it to go.

“Who are you?” demanded Hazelton, once more, as he stepped cautiously forward.  “No use in your keeping silent, my man.  I see you and know that you’re there.  Moreover, I’m going to drag the truth out of you as to what you’re doing out here on the wall at this hour of the night—–­and to-night of all nights.”

Still no answer; Harry went steadily forward, until he was within a dozen feet of the head of the flattened brute in human guise.  Hazelton could now see every line of his adversary plainly, though he could not make out the fellow’s face.

“You’d better get up and talk,” warned Harry, poising the rock fragment for a throw.  “If you don’t you’ll cast all the more suspicion upon yourself.  For the last time, my man, who are you and what are you doing here?”