Left by himself Harry had stood, at first, motionless, or nearly so.  He strained his hearing in trying to detect any unusual sound of the night, since it was so dark that vision would not aid him much.

There was nothing, however, but the mournful sighing of the wind and the lapping of the waves.  It seemed to Hazelton that the wind was growing gradually more brisk and the waves larger, but he was not sure of that until the water commenced splashing across his shoes.  The footway on the masonry became more slippery in consequence.

“With these rocks well wet down I wouldn’t care much about having to run back to the land,” muttered Harry, dryly.  “However, I won’t have to go back on my own feet.  Tom will have the boat out here, and undoubtedly he will plan to have us both taken back to shore after we get through cruising around here.  We should have brought the boat out in the first place.”

A night bird screamed, then flapped its wings close to Harry’s face in its flight past him.  The young engineer saw the moving wings for an instant; then they vanished into the black beyond.

Farther out some other kind of bird screamed.  The whole situation was a weird one, but Harry was no coward, though a less courageous youth would have found the situation hard on his nerves.

Still another night bird screamed, of some species with which Hazelton was wholly unacquainted.  The cry was answered by some sort of strange call from the shore.

“It’s a fine thing that I’m not superstitious,” laughed the young engineer to himself, “or I’d surely feel cold chills chasing each other up and down my spine.”

As it was, Harry shivered slightly, though not from fear.  With the increasing wind it was growing chilly out there for one who could not warm himself with exercise.

“It’s a long time, or it seems so,” muttered the young engineer presently.  “Yet I’ll wager that Tom is hustling himself and others on the very jump.”

Again the call of a night bird, and once more a sound from shore seemed to answer it.

“Real birds?” wondered Hazelton, with a start of sudden curiosity.  “Or have I been listening to human signals?  If so, the signals can’t cover any good or honest purpose.”

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?”

The huge black figure might have been a log for all the answer that came forth.

“All right, then; it’s your own fault,” Harry Hazelton continued calmly.  “As you won’t speak I’m going to crack the nut for myself.  Your head will be the nut, and this rock I have in my hand shall be the hammer.  I’m going to slam this rock on your head with all the force I’ve got, and I’m a good, straight thrower.”

Yet, though Hazelton spoke with such confidence, he was far from meaning all he said.  In the first place, he had no legal right, under the circumstances, to go as close to murder as it might be for him to throw the rock at the rascal’s head.  Moreover, Harry would hardly have exercised such a legal right, had he possessed it, without the strongest provocation.

From the black prowler came a sudden, fierce snort.  It sounded altogether like defiance.

“Ho-ho!  You’re finding your voice, are you, my man?” Hazelton jeered.  “Then talk up in time to save yourself!”

Instead the huge black man began to writhe forward.

“Stop that!” ordered Harry dangerously.  He did not retreat from the writhing human thing, but he took better aim, noting that the black man was hatless and that his head offered a fair mark.  “You’re going to get hurt in just about a second more,” he added.

Uttering another snort the bulky black sprang to his feet with surprising agility in one of his great size.

Harry now let his right hand fall back quickly.  He was poising for the throw in earnest, for there could no longer be any doubt that the stranger was planning a deadly assault.

“Take it, then, since you want it!” snapped out Harry Hazelton.  The fragment of rock left his hand, propelled with force and directed with accurate aim at the negro’s face.

But the crafty black dodged just in time, at the same instant throwing up his hands.

Harry gasped as he saw his unknown assailant deftly catch the rock fragment as though it had been a base ball.

“Ha, ha!  Ho, ho!” jeered the black, in a hoarse, rumbling voice.

He threw back his hand, gathering impetus for the cast.  Hazelton could do nothing but throw himself on the defensive, planning to duplicate the black man’s catch.

Then the stone came-but it did not go high, instead, by a jerk of his wrist, the negro hurled it at Harry’s right foot.

That granite-like fragment struck Hazelton’s foot with full force.

“You-you scoundrel!” groaned Harry, in an all but admiring gasp.

Like a flash he bent over, snatching up the fragment for his own use.

“Now, I’ll slam you into the middle of the Gulf of Mexico!” cried the young engineer, vengefully, as he tried to straighten up.

A groan escaped him.  His injured foot was paining him more than he had expected.

“Ha, ha!  Ho, ho!” harshly jeered this mysterious, evil creature.  The black man had halted as Harry prepared to throw, but he showed no sign of hesitation.  Though he stood still, he thrust his repulsive, leering face forward, as though to offer that face as the best mark.

Harry found that he could not stand straight-the pain in his injured foot was now too intense.

“Get back with you!” ordered Harry.  “Get back if you don’t want a heap worse than you gave me.”

“Ha, ha!  Ho, ho!” came the sneering laugh.  Then the stranger reached out his hands as though to seize the youth.

“I guess I’ll have to do it-though not because I really want to hurt you!” muttered Harry ruefully.

“Ha, ha!  Ho, ho!”

There could be no question that the unknown was merely playing with him.  Little as he liked to make the ugly throw Harry knew that he had to do it.  When Hazelton had anything to do he believed in doing it well.  So, putting all possible force into his throw, Harry let the rock fragment fly, and this time he was sure that his enemy would not be able to dodge in time.

Nor did the black man make any seeming effort to dodge.

Bump!  Squarely in the black face the rock landed.  Harry heard the sound and felt ill within himself.  Yet the black man did not stagger.  With a contemptuous snort he kicked the fragment of rock into the water as it landed at his feet.

“Ha, ha!  Ho, ho!”

For the first time Harry Hazelton felt positively dismayed.  He saw the long, massive arms moving, looking like a powerful ape’s arms.  There could be no doubt that the unknown was ready for a spring.

Harry did not retreat.  Where could he run to?  Only a few yards could he go out towards the end of the wall.  Then, if he wished to continue his flight he could only take to the water.

Only a glance was needed at the bulky, powerful frame of the unknown to make it appear certain that the latter could swim two rods to the young engineer’s one.

Harry decided instantly to stand his ground and to make the most valiant fight possible on so slippery a footing as that presented by the top of the retaining wall.

“Ha, ha!  Ho, ho!”

It was as though the black unknown sought to terrify his intended victim with his repetitions of that harsh, discordant laugh.  Harry braced himself and waited.

Then, off shoreward, came the sound of “put-put-put.”  The motor boat, “Morton,” was putting out at last.

“If I can keep this fellow busy for a few minutes, I can have all the help I want,” flashed through Hazelton’s mind.  So he opened his mouth, raising his voice in a long, pent-up hail.

“R e-e-e a d e!  To-o-o-om R e a d e!  Quick!  Hazelton!”

“Ha, ha!” jeered the unknown black.

Then, suddenly, he leaped-not unexpectedly, however, for Harry had been watching, cat-like.

The unknown threw out his arms, seeking to wrap them around Hazelton.

Not in vain had Harry been trained, season after season, on the athletic ground of one of the best high school elevens in the United States.

As the fellow leaped at him Harry crouched lower and went straight at his opponent.

Powerful as the stranger was he was no football player.  Harry “tackled” him in the neatest possible way, then strove to rise with this great human being.

In the first instant it seemed to the young engineer as though he were trying to lift a mountain.  His back felt as though it were snapping under a giant’s task.  Yet, but for one fact, Hazelton would have risen with his man, and would have hurled the mysterious one over into the waters of the gulf.

Just in the instant of victory Harry’s injured right foot gave out under him.  With a stifled groan he sank down just as he threw his opponent.

The black, instead of going into the water, landed hard on his back on the top of the wall.  He was up again, however, before Hazelton could repress the pain in his foot and leap at the wretch.

“Ha, ha!  Ho, ho!” came the tantalizing challenge.

“Put-put-put!” sounded over the water, coming nearer all the time.

“Re-e-e-e a d e!  T o m R e a d e!  Help-quick!” yelled Harry, lustily.

This, doubtless, was the first call that Tom, at the bow of the motor boat, thought he heard.

Uttering a snort, this time, instead of the laugh, the black sprang at his intended prey.  Their heads met, with considerable force.  Then, with a wild chuckle, the black wound his apelike arms around the young engineer.

“Reade!  Tom Reade!  Reade!” bellowed Hazelton lustily, as he tried desperately to free himself from the crushing embrace of the other.

Over the waters came the penetrating beam of a small search-light.  The “Morton” was coming nearer all the time, but the ray did not yet reach with any great clearness the point where Harry Hazelton had been fighting for his life against his strange foe in the black night.

“Keep parallel with the wall, Evarts,” Tom ordered, crisply.  “Conlon, are you pushing the engines for all it’s worth?”

“Yes, sir,” came from the engine-tender.  “This old craft isn’t good for quite seven miles’ an hour, anyway.”

“There!  Now I’ve picked up the part of the wall where there isn’t any wall in sight just now,” said Tom, wincing over his own bull.  “Hazelton ought to be just this side of there.”

“There’s no one near the breach,” replied Evarts.

“So I see,” Reade admitted, in a tone of worriment.  “Oh, well, Harry isn’t such an infant as to be wiped out all in one moment.”

“Where is Mr. Hazelton then?” inquired Evarts, as Tom swung the arc of the searchlight in broad curves.

“Great Scott!  I wish I knew!” gasped Reade, his perplexity and his anxiety growing with every second.  “There appears to be no one on top of the wall.”

Evarts ran in within a few feet of the wall, on the shore-side of the breach.

“Shall I land you there, sir?” questioned the foreman.

“Presently,” Tom nodded.  “But now, back out a few feet and swing the boat’s nose around so that I can make a search with this light.”  Evarts obeyed the order.  Despite the smallness of the light, Reade was able to send the searching beam of light back nearly one-half of the way to shore.  Nowhere was there any human being visible on the wall.

“Harry!  Hazelton!” bawled Tom, with all the power in his lungs.

There was no answer.

“Jupiter!  You’ll have to land me, I reckon,” quaked Tom Reade.  “Drive her nose in-gently.  I’ll be ready to jump.”

“Be careful how you do jump,” warned Evarts.  “It’s mighty slippery on that wall tonight.”

Tom poised himself as the boat moved in close.  Then he took a light leap, landing safely.

Here the young chief engineer again brought his pocket flash lamp into play.  Closely he scanned the top of the wall all around where he knew he had left his chum.

But Harry was nowhere to be seen, nor, on the wet wall, could Tom find any signs of a scuffle, or any other sign that gave him a clue.

“Evarts, this is mighty mysterious!” groaned the young chief.

“Unless-” hinted the foreman.

“Unless what?”

“Perhaps Mr. Hazelton ran along the walltop to the shore.”

“He’d have hailed us, then, in passing, wouldn’t he?” choked Tom Reade.  “Besides, I had the light playing on this wall most of the way.  If he had run back we would have seen him, even if he hadn’t hailed.  And he couldn’t have run farther out to seaward.  Evarts, I’m downright worried.”

Tom Reade might indeed well be worried over the grewsome mysteries of this night of evil deeds.