Towards morning the fire dwindled and went out. At daylight they could see no sign of von Hardenberg and his companion. The entire valley appeared deserted. In this part of the country there were no villages, the valleys being too barren and infertile for agriculture.

The next night the bivouac-fire was again visible, this time nearer than before. On the third night they were not more than seven or eight miles in rear of those whom they pursued.

On these occasions they were careful that their own fire should not be observed. They always lit it under the cover of large rocks or boulders, screening it from the north. They had every reason to suppose that the sheikh and his companion believed them dead. The Black Dog had doubtless told his employer that their pursuers had been buried alive in the crater of the old volcano.

Every night they were careful to post a sentry, and, on one occasion, when the first signs of dawn were visible in the east, Harry-who was on watch-suddenly heard a sound, faint but very distinct, immediately behind his back.

He turned quickly, but could see nothing. He waited for some moments, holding his breath, with his finger ready on the trigger of his revolver.

Nothing happened. The boy imagined that the sound had been caused by a rock-rabbit or a mountain-rat, and was about to resume his former position, when something descended upon him with a spring like that of a tiger.

In the nick of time he jumped aside. He saw a white figure rushing violently through space. In the moonlight he saw the flash of a knife that missed him by the fraction of an inch, and the next moment he was full length upon the ground, struggling in the arms of a powerful and savage man.

Locked together in a death-grip, they rolled over and over, first one on top and then the other. There was a loud shout, which came from the lips of Braid, and at that the two guides sprang to their feet and hastened to Harry's assistance.

The struggle ended as suddenly as it had begun. One second, strong fingers gripped Harry by the throat, and the next his adversary was gone. He had vanished like a ghost; he had slipped away like an eel.

Harry Urquhart sprang to his feet and listened. He heard a laugh-a wild, fiendish laugh-far away in the night. Stooping, he picked up a bare knife that was lying on the ground.

"I wrenched this from his hand," said he, showing the knife to Fernando.

The half-caste examined it in the firelight. It was a knife of Arab design.

"That," said he, "is the knife of the Black Dog."

"Why did he not fire?" asked Harry.

"Evidently because he did not wish to warn the Germans. That is a bad sign; it means that the German troops are in the neighbourhood."

The following night, when they scanned the valley, they could see no sign of the camp-fire of von Hardenberg and the Arab. The sheikh, having failed in his enterprise on the previous evening, was evidently determined to exercise greater caution. Harry examined the valley with his glasses, not only to the north but also to the west and to the east. However, he could see no sign of their enemies.

"I do not like the look of it," said Fernando. "So long as we knew where the Black Dog was, we had the whip hand of him. We must be prepared for the worst."

"Surely," said Harry, "he will push on towards Maziriland?"

"The shortest way is not always the quickest," answered the other. "As likely as not he has gone back upon his tracks, and even now is encamped somewhere behind us."

That night they deemed it advisable to light no fire. Seated amid the rocks on the crest-line of the hills, where the wind moaned and howled from the west, they held a council of war. It was decided that, during the march on the following day, the two guides should act as scouts, the elder moving some distance in advance of the three Europeans, Cortes following in rear.

By the time the sun rose above the mountain-tops, they were well upon their way. At mid-day they halted for a meal, and it was then that Cortes came running to the bivouac.

"Come here!" he cried. "I have seen them."

They followed the man to the crest-line, crawling on hands and knees. Only Peter Klein remained by the fire. Since they had escaped from the crater of the volcano no one had spoken to the man. The guides showed only too plainly that they despised him, and neither Harry nor Braid were disposed to forgive the scoundrel for having stolen their last drop of water.

They came to a place where the valley-side dropped down in an almost perpendicular cliff. Far below was a little grove of trees, around which a stream meandered, its waters glistening in the sunshine. Beyond the grove, on the other side of the valley, following a kind of bridle-path that led to the north, were five men, one of whom was dressed in robes of flowing white.

"That is the sheikh," said Fernando. "He walks by the side of the German."

"And the other three?" asked Braid.

"They are natives from the bush. The sheikh has doubtless enlisted their services during the last three days. The natives dare not refuse him labour. He was all-powerful when he was a slave-trader; fear of him passed from village to village by word of mouth. On an expedition such as this, he is doubly to be dreaded, because he has friends among the Maziris themselves."

"Then," cried Harry, "supposing he tells the tribe to rise against us?"

"There is little fear of that," said Fernando. "He is hated by the chiefs and head-men, who resent the authority he wields over many of the people."

"Then, what will he do when he draws near to the caves?"

"He will rob by night," said Cortes. "Under cover of darkness he will endeavour to secure the treasure."

"My brother," said the elder man, laying a hand upon the other's shoulder, "tell me, how far away is Black Dog?"

The man judged the distance with his eye.

"Sixteen hundred yards," said he.

"Nearly a mile," said the other. "I will try my luck. I have sworn an oath by the saints."

So saying, he lay down upon his face and loaded his rifle. Lifting the back-sight, he took long and careful aim, and then pressed the trigger. There came a sharp report, and the bullet sped across the valley.

In the space of a few seconds the sheikh and his followers had vanished. To hit a moving figure at that distance was a well-nigh impossible task, but that the bullet had not been far from its mark was apparent from the way in which the party had so suddenly disappeared.

Von Hardenberg was moving up one side of the valley, Harry and his companions on the other. It was therefore a race for the treasure. If Harry reached the caves first, he would be unable to enter the vault, by reason of the fact that the Sunstone was not in his possession. He would have to lie in wait for the Black Dog and the German.

For two days they saw nothing more of their rivals. There was water in plenty in the district, and presently springs and streams became even more numerous, and they entered into a country that was thickly wooded. At the same time the mountains became more wild and rugged, and it was soon impossible to make progress by way of the hills.

They therefore descended into the valley, and entered a region of scattered trees, which gradually became a forest, where they were shut out from the sunlight and the light of the stars. There were no paths in the forest, and they could seldom march more than eight miles a day by reason of the tangled undergrowth through which they had to cut a passage.

When they came out of the forest they were in a land of rolling hills, which, the guides told them, mounted to the summit of Maziriland. Their first camp in this district was under the lee of a hill; and, since they had seen nothing of either von Hardenberg or the German troops for several days, they deemed it safe to light a fire. There was no scarcity of fuel, and very soon a fire was blazing, the green wood crackling and hissing in the flames. Over the fire a kettle was suspended by a chain from three iron rods, and from the spout of this kettle steam was issuing, when suddenly a shot was fired in the distance, and a bullet drilled a hole through the kettle, so that the water from within ran down into the fire, whence issued a little cloud of steam.

CHAPTER XVIII-A Dash for Liberty

As one man they rushed to their arms, and even as they did so a score of shots rang out, and the whistling bullets cut the earth about their feet.

"The German troops!" cried Cortes. "We must gain the hill-top or we're lost!"

Firing into the darkness as they ran, they ascended the hill with all dispatch. At the top they found themselves subjected to a withering fire, which poured down upon them from all directions. The night was alive with the sharp reports of rifles. Sudden flashes of fire showed up on every hand, like so many living tongues of flame. It was evident the enemy was in force.

For four hours the fight continued without a check. The roar of the musketry continued; the hissing of the bullets was like heavy rain. And all this time the German soldiers were working nearer and nearer, until at last they formed a complete circle around the foot of the hill.

They were then close enough for their voices to be audible, and now and again, as a bullet found its mark, a shriek went up in the night.

By then, not one of Harry's party had been struck. This was partly due to the boulders which lay upon the hill-top, and behind which it was possible to obtain cover, and partly to the inferiority of the German marksmanship.

During a lull in the combat, a short respite from the strain of the situation, Harry took counsel with the two guides and Jim.

"It appears to me," he observed, "that if we wait till sunrise we are lost. So far, we have managed to escape death only by reason of the darkness."

"Before the sun rises," said Fernando, "two courses lie open to us: we must either fight our way through the enemy or commend our souls to Heaven."

"I was going to propose," said Harry, "that we gather together in a body and endeavour to charge through the enemy."

"And after that?" asked Braid.

"After that we may either find some place more suitable for defence, or else die in our tracks."

"We can die fighting," said the younger guide.

"Well, then," said Harry, "every minute counts. If we can get through we may be able to cover some miles before dawn is upon us. We must hold together, however. There will be no time to go back to look for one who is lost."

They now prepared themselves to make this last and desperate bid for freedom. They played for the highest stakes, for liberty and life. They could not advance, however, without acquainting Peter Klein of their intention, and when the man was told of what they proposed to do he set to shaking in his limbs.

Harry was in no mood to humour him. He had long since lost all patience with their uninvited guest.

"You have two minutes," said he, "in which to choose. Either you come with us, or stay here, or else you can go over to the enemy. It does not matter very much to us which you decide to do."

The man picked up his rifle. He tried to speak, and stuttered. He was incoherent from fear, though it was his own countrymen who opposed them. German and German-trained native troops were in the valley in about equal numbers.

"What am I to do?" he asked.

"Remain at my side," said Harry. "Do not fire until I tell you to. We are going to creep as near to the enemy as we can, and then charge through together."

Klein said nothing, but they heard the bolt of his rifle shake in his hand.

Then all five began to crawl down the hill, picking their way carefully over the stones, advancing as stealthily as possible.

The enemy's fire had somewhat abated. Perhaps they also-true to the traditions of the Prussian army-contemplated an assault. Instead of the continuous rattle of musketry that had lasted for so long, only an occasional shot resounded in the valley.

Inch by inch, they drew nearer to the enemy's position, and when not twenty yards from the place where a German officer was shouting hoarse, guttural words of command, Harry whispered to his followers to halt. He desired to give them time to gain their breath, that the charge might be as swift as it was sudden and unexpected.

During the next few minutes it was as if each second dragged out into eternity. At all events, the anxiety and excitement had the most amazing effect upon Peter Klein, who was a coward from the day of his birth. It drove him mad, and he became like some infuriated beast, a bull in a bull-ring or a baited bear.

Suddenly springing to his feet, before Harry had given the word of command, he discharged the magazine of his rifle in the direction of his own countrymen. Then, seizing the weapon by the muzzle, he dashed down hill, swinging it round and round his head as a man uses a club.

Harry and his three companions followed in the man's wake, firing right and left. Though it was dark, they were near enough to Klein to see what happened. The man was as terrible in his madness as he had been despicable in fear. Without a doubt, terror had overcome his senses. Giving himself up for lost, he had been able to bear the suspense no longer, and now rushed furiously, demented and panic-stricken, into what looked like certain death.

A German sergeant jumped out of the grass before him, and the butt of Klein's rifle crushed the man's skull as though it were a nut. Another man-a native-a second later was dropped to the ground, with a blow that would have felled an ox. A third rushed upon the maniac, and so tremendous was the stroke that sent him to his death that Klein's rifle broke at the small of the butt.

Still the ex-spy was undefeated. With the steel barrel in one hand and his revolver in the other, he went onward in the dark, filling the night with an infinity of savage and appalling yells.

CHAPTER XIX-War to the Knife

Ten minutes later Peter Klein stopped dead, looking about him with wild, staring eyes. The night was cold-for they were still at a great altitude-and the breath was pumping from his nostrils as it does with a horse. However, he was given little time to rest, for Harry, running forward, seized him by the arm.

"Get on!" cried the boy. "We're not out of danger yet."

On they went, racing for freedom, crossing hills and minor valleys, passing beneath trees, and sometimes knee-deep in the water of forest streams.

For a time they heard the guttural voices of the Germans behind them. At last these became inaudible in the distance. The soldiers were not able to follow on their tracks, since they had no way of knowing which route the fugitives had taken.

At last Harry deemed it safe to call a halt.

Klein, who was still running like one possessed, had to be stopped by force. He would not desist from flight, until Jim Braid had tripped him up. Harry, followed by Fernando, came upon them shortly afterwards.

"See," cried Harry, pointing to the east, "there comes the dawn! In half an hour it will be daylight."

"Do you know where we are?" asked Braid, turning to the guide.

"Yes," said the man. "We are towards the Maziri frontier. I recognize the mountains on the sky-line. There is a good place near at hand where we can hide, and where-even if we are discovered-we will be able to hold our own for many days."

"Let us go there," said Harry. "But where is your brother?"

No one answered. They peered into the faces of one another. The younger guide was missing.

Fernando, the man who had sworn an oath to kill the Black Dog, lifted his hands to his mouth and let out a long-drawn howl which was like that of a jackal, and which carried far in the stillness of the morning. It was a signal that his brother knew of old. Three times he repeated it, and each time lifted a hand to his ear, and stood listening expectant.

No answering cry came back. A death-like silence reigned over the valleys and forests and the mountain-side.

"He is lost?" asked Harry.

"He may have taken the wrong direction in the darkness. He may have been struck by a bullet. Who can tell? These things are in the hands of God."

"He may be somewhere near at hand," said Braid, hoping for the best.

Fernando shook his head.

"If Cortes is alive he is far away; otherwise he would have heard my signal. At any rate we can do no good by waiting here. We must push on; the day approaches. As I said, I know of a place where we shall be safe."

As the grey light extended from the mountain-tops to the valleys, Fernando led them to a kind of ancient fort, constructed of great stone boulders and surrounded by a deep ditch. In the parapet of this fort there were loopholes through which to fire, and in the centre, well screened from observation, was a small hut made of the branches of trees. The redoubt stood on a sharp pinnacle of rock commanding a wide stretch of country on every hand. It had doubtless been constructed centuries before, when there was a more advanced stage of civilization in the heart of Africa. Indeed, it is from this bygone civilization that the Maziris themselves trace their origin.

As the daylight increased they were able to take in their surroundings. Many miles up the valley, it was just possible to see a little village, which, Fernando assured them, was in Maziriland itself. Some distance to the west was a great forest which extended as far as the eye could reach.

Harry looked around him in amazement.

"But this place is almost impregnable," he cried. "Four resolute men could hold it against hundreds."

"Is there water here?" asked Braid, turning to the guide.

The man pointed to a small spring which bubbled up to the surface near the door of the hut.

"I will tell you the story of this place," said he. "Years ago a party of six Maziris sought refuge in this fort, which was built in the olden times, when the Ancients crossed the deserts from the east. For eight months those six men held the army of one of the Cameroon kings at bay. They had laid in a great store of food. They made the defence even stronger. Time and again they beat back the attack."

"And in the end?" asked Jim.

"In the end four of their number were killed, but the other two escaped."

"Escaped! How did they escape?"

"You will not believe me, but it is true. They escaped underground-like moles."

"Underground!" cried the two boys, echoing the man's words in their astonishment.

"Yes," said the guide. "All those months they had been digging a tunnel. The hill is composed of a very soft kind of rock; and they had brought spades and picks from Maziriland. Day and night they worked, until at last the tunnel became a mile in length, extending from the inside of the fort into the very heart of the forest."

"Where is the entrance?" asked Harry.

"It is here."

The man led the way to the hut. The floor was covered with rushes, and these he gathered together in his arms and piled in a great heap before the doorway. Underneath was a circular piece of wood, like that which is often found on the top of a well. Lifting this, Fernando pointed to a flight of steps that led down into impenetrable darkness.

"They went this way?" asked Harry.

"Two escaped by way of the tunnel, whilst a third, who was already dying, covered up the entrance with rushes. When their foes got in they found only four men-dead. And they believed that they had been held at bay during all those months by four men instead of six."

"Does your brother know of this place?"

"Yes; and if he is alive he will guess where we have gone. He will come to us by way of the tunnel. If he is dead-" And Fernando shrugged his shoulders.

During that day and the next they saw nothing of the Germans; but Fernando protested that it would not be safe to push on towards Maziriland, since the enemy was certainly in the district. Also they still hoped that Cortes would return.

During these days they were not idle. Jim Braid was left behind in charge of Peter Klein, who could not be trusted to hold his own in case of sudden attack, whilst Harry and Fernando departed into the forest by way of the tunnel.

The long journey through the subterranean passage was one of the most unpleasant experiences that Harry Urquhart ever had in his life. Not only was the place pitch dark, but water had filtered through the walls and lay here and there in pools upon the floor. These pools had grown stagnant, and the air was humid, tainted with the foulest smells.

At last, they came forth into the forest. There, for two days and one night, they collected a great store of provisions. They dared not fire their rifles, but there was no necessity to shoot. The forest abounded in ground-nuts and various kinds of fruit. Also, Fernando knew where the natives set their traps, and the two devoted their time to robbing these, until finally they had sufficient supplies to last for several days-rabbits, small hog-deer, and many kinds of birds.

They were obliged to make three journeys to the fort with all the provisions they had obtained, since it was not possible to carry a heavy load through the narrow, stifling tunnel.

On the third day they set to work cutting up the meat and drying it in the sun. Sun-dried meat is uncommonly tough, but it has this advantage-it will keep for many months.

That evening they heard a shot far away in the distance. It was followed by another, and yet a third, and towards midnight the whole valley was alive with musketry.

"What is it?" asked Harry of the guide.

The man shrugged his shoulders.

"I cannot say," said he. "Either my brother is pursued by the Germans, or a fight is taking place between them and the Black Dog-in which case I may be robbed of my revenge."

They divided the night into three watches. Peter Klein, they knew, they could not trust in any responsible position requiring strong nerves and presence of mind. They set the man to the most menial tasks-chopping wood, cooking, and repairing the ancient defences.

All night the firing in the valley continued; by daybreak it was near at hand. They could see the figures of the Germans racing across the valley, advancing in extended order or else in small groups which at that distance resembled families of mice.

That afternoon a small reconnoitring-party of the enemy ascended the hill upon which stood the fort. The defenders lay in hiding behind the parapet, determined not to show themselves, not to disclose their hiding-place, unless it was certain that the Germans intended to occupy the hill-top.

They waited till the eleventh hour. The enemy was not twenty paces from the ditch when Fernando rose to his feet, and cried out in the German language, ordering them to halt on peril of their lives.

At the same time, he raised his rifle to his shoulder and sent a bullet over their heads. As one man they turned and fled, racing towards the forest, and were lost to sight.

It was from that moment that the siege commenced. Their place of refuge became a citadel encompassed on every hand by a hostile force. The Germans gathered round them in companies, and day and night strove to induce the garrison to surrender. It was trench warfare in the heart of the African wild.