The Germans soon found that it was impracticable to attempt to capture the fort by a direct frontal attack in daylight. The slope of the hill was so steep that it was possible to ascend only by way of a path which was covered by the rifles of the defenders. Apparently they had no artillery at their disposal.

At first they charged up this path after the manner in which they were wont to hurl themselves upon the lines of trenches in Poland and in Flanders. They were swept down like chaff. Owing to the narrowness of the way they were obliged to advance upon the fort in single file, and as each man appeared before the loopholes he paid the price of his daring.

After the first assault they resorted to tactics more likely to succeed. They attacked twice by night. But, fortunately for the defence, the nights were fine and starry, a full moon was up, and it was possible to see the enemy long before he reached the walls of the fort.

For all that, the greatest vigilance was necessary both by day and night, to avoid being taken by surprise. One or other of the defenders was always on guard. Even Peter Klein was of some use. Though he could not be relied upon to act with courage or promptitude, his eyesight was good enough, and he took his turn at sentry by day. Moreover, he was in such abject terror of falling into the hands of his own people that Harry suspected that the German authorities at Dualla had learnt something of the Sunstone and von Hardenberg's private mission to the Cameroons.

By night, when the fort might be rushed, they thought it best not to leave their destiny in the hands of one who had failed them so constantly. The only occasion on which Klein had covered himself with credit was at a moment when fear had so possessed him that he lost all sense of danger and became for the time being a raving madman.

It would be wearisome to describe the details of the siege as it continued day by day. There is no question that the defenders would have held their own for many weeks had it not been that gradually a calamity was drawing down upon them. They were running short of ammunition. Their bandoliers were nearly empty.

The Germans kept up a constant fire upon the fort, and the garrison, in self-defence, was obliged to answer back. They calculated that, with the greatest economy, they had cartridges sufficient to last them only four days more. It was then that Klein, Harry, and the guide entered the hut and held consultation together. Jim Braid was on sentry, stationed on the parapet. The sun was setting in the west.

It was Fernando who was the first to speak.

"The situation is very plain," said he. "We can hold out until our ammunition is exhausted, and then retire by way of the tunnel, still hoping to reach the caves in advance of von Hardenberg, or we may retire to-night.

"Which do you advise?" asked Harry.

"I suggest," said the guide, "that we go at once. We shall need ammunition on our return journey to the coast. We have many miles to traverse. Every moment we delay means a further expenditure of ammunition. We have not a cartridge to spare."

"Then," said Harry, "it is settled: we leave the fort this evening."

It was then that there came a loud and sudden burst of firing from down the valley, from the direction of the forest. All three sprang to their feet.

Braid, from the parapet, called loudly, and they hastened to his side.

"Look there!" he cried.

Turning their eyes in the direction indicated, they beheld a man running as if for life towards the forest. In pursuit, some distance in his rear, came a large party of Germans, shouting so loudly that their voices were audible even at that great distance, and firing their rifles as they ran.

"Who is it?" cried Harry.

"I cannot say," said the guide. "He is too far away."

The firing continued until long after nightfall. It rolled through the forest like a wave. It was not until ten o'clock that the night was still.

The four defenders gathered at the door of the hut.

"You think it wiser to go?" said Harry

Fernando bowed his head.

"Come, then! Let each man load himself with such provisions as he can carry. We should start at once. It is necessary for us to be far away before morning."

Harry Urquhart turned and was about to enter the hut, when he was brought to an abrupt standstill. He stood motionless and gaping, unable at first to believe the evidence of his own eyes. For there, in the doorway, within the enclosure of the fort, stood the figure of a man-a man who was dressed in robes of flowing white.

"The Black Dog!" let out the guide, and brought his rifle to his shoulder.

"Peace," said the sheikh, lifting a hand. "Think before you fire."

Fernando's rifle was directed straight at the man's heart. The Arab never flinched. He stood like a statue, speaking in the slow, deliberate tones of one who is in full possession of his senses.

"If you fire," said he, "you slay one who has come to place his services at your disposal. You are surrounded by a legion of foes. Every rifle counts. I bring you aid."

Slowly Fernando lowered his rifle; then he laughed.

"We do not want your aid," said he.

"There," answered Bayram, "you are wrong."

"How so?"

"Here you are imprisoned. You must fight to the end. There can be no question of surrender."

"We do not think of surrender," said the other. "We mean to escape by the way you came. We mean to escape to-night."

The Black Dog shook his head.

"That will not be so easy," he made answer. "The Germans are receiving reinforcements; another column is advancing from the south. The bush swarms with their reconnoitring-parties and patrols. Moreover, guns are approaching up the valley, and may be here at any moment. I speak the truth. Remember, at some risk I have come here of my own accord."

He spoke slowly, as if choosing his words with care; but his English accent was singularly good.

"You have not yet told us," said Harry Urquhart, "why you have come."

"You are short of ammunition," answered the sheikh.

"How do you know that?"

"For five days I have listened to every shot."

"You have not yet explained," said Harry.

The Black Dog smiled, his white teeth showing in the midst of the blackness of his beard.

"I come with a proposal," said he, "under a flag of truce."

"You have nothing to fear," cut in Fernando. "You speak of a truce. We are men of honour."

"Very well, then," said the sheikh, "my proposal-or rather the proposal of him who sent me-is that your party and mine agree to come to terms. You have run out of ammunition; we can supply you. Boxes of ammunition can be conveyed without difficulty through the tunnel. Moreover, in order to cover your retreat, I swear by Allah that I will lead the Germans on a false scent across the mountains to the east."

"And in exchange for these services?" asked Harry.

The Black Dog paused, looking hard at Fernando.

"In exchange for these services," he repeated, "you are to desist from the pursuit, to allow my employer and myself to pass unmolested in Maziriland."

At this base suggestion, a feeling of such powerful indignation arose in Harry Urquhart that for some moments he could not find his voice. When he spoke at last, his voice trembled with passion.

"You can go back to Captain von Hardenberg," said he, "and you can tell him from me that he has often enough proved himself a rascal, but that I never thought that he would sink to such perfidy as to offer us ammunition to be used against his own countrymen in exchange for his own safety. As for you, it is only because you came here of your own free will that you are allowed to go away in safety. You took us evidently both for cowards and fools. You know now, perhaps, that we are neither one nor the other. But there is a limit to our patience, and I advise you to leave by the way you came as quickly as you can."

The Black Dog drew himself up to his full height, folded his arms, and fixed upon Harry Urquhart his cruel bloodshot eyes.

"These are high words," said he, "to one who has been the master of a thousand slaves. You have asked for war to the knife, and you shall have it. It is apparent from the way in which you speak that you know little or nothing of the man with whom you have to deal. You shall see. I shall prove to you that I am not one who uses empty words."

At that he turned sharply on his heel, entered the hut, and was gone.

CHAPTER XXI-The Last Cartridge

During the next four days the siege continued, and though their enemies continued to increase in numbers, the Germans were fortunately still without artillery, which would have battered the old fort to dust and ashes in the space of half an hour.

On each occasion when the Germans ventured to assault they were driven back with considerable loss. Indeed, their dead lay so thick upon the path upon the hill-side that those who followed after mounted on the bodies of those who had gone before.

On one occasion a company of native troops actually gained the parapet of the fort. It was a dark night, and they had crept up the hill-side unobserved. With a savage yell, and as one man, they hurled themselves upon the ramparts.

The majority were thrown back in disorder under a brisk fire from the defence, but some half-dozen leapt the ditch and clambered over the wall. Thereupon a brief hand-to-hand encounter ensued. It was an affair of seconds, of fierce cries and groans and savage oaths, and in the end the enclosure of the fort was free of the enemy-except for six motionless forms that lay silent on the ground.

Days passed, and still the defence held out. Indeed, they had actually put off their retreat until too late, for one night they were brought face to face with the unexpected fact that the Germans had discovered the entrance to the tunnel. Fernando, who had passed almost to the mouth of the tunnel, which lay in the midst of the bush, returned to the fort with the news that a large party of German regular soldiers was guarding their only line of retreat. Fernando had little doubt that the Black Dog had found some means by which to betray them.

The Germans apparently hesitated to advance through the tunnel itself, since they were still in ignorance of the strength of the little garrison; and in any case the narrowness and exceeding darkness of the passage would make an advance an extremely costly affair, whereas ultimate success was by no means assured. They could no longer be blind to the fact that those in the fort were running short of ammunition, and they could afford to play a waiting game.

The situation of Harry Urquhart and his companions was not of the pleasantest; indeed, they could no longer hope. Even Fernando, who had so often proved himself a man of iron, could see no chance of their deliverance.

As a great storm drives up upon the wind, so this tragedy drew to a close. Every round of ammunition-fired in self-defence-every mouthful of food that was eaten, brought it a step nearer the end. They were surrounded on every hand. Great numbers of the enemy had come from the south; both German and native troops were in the district in battalions, with transport and ammunition columns and machine-guns.

By then it was manifest that the Germans could capture the fort whenever they wished, provided they made the necessary sacrifice in lives-a thing which, as a rule, it is not their custom to hesitate to do. They had not yet, however, deployed their whole strength against the garrison-a fact that Harry was not able to explain.

The blow, which they had anticipated for days, fell upon a certain morning, soon after daybreak, when the Germans, their whole force in the valley, advanced in close formation upon the fort.

At the same time a battery of artillery opened fire from the neighbouring hills, and the immediate vicinity of the fort became a pandemonium of dust and smoke and flying stones and masonry, whereas the defenders were well-nigh deafened by the bursting of high-explosive shells.

In spite of this hurricane of lead and steel, time and again shots sounded from the fort; but the great wave came on, overwhelming and irresistible. One behind the other the ranks mounted the path. The defenders kept up a withering fire, until the barrels of their rifles were so hot they could not touch them. And still the enemy advanced.

As the Germans gathered themselves together for a final charge, Harry, Jim Braid, and the half-caste rushed together from the parapet to the only box of ammunition that remained. The box lay open near the door of the hut. Fernando was the first to reach it.

He pulled up sharply, standing motionless and erect. Then he knelt down and took out from the box the only cartridge that was there.

"This is all that is left," said he.

"No more?" cried Harry.

"We have come to the end," said the guide.

Jim Braid turned and addressed his companions.

"Has no one any ammunition?" he asked, and in his voice was a note of dire distress.

Both shook their heads. Peter Klein was cowering in the hut.

"This is all that remains," said Fernando. "It shall be put to excellent use."

So saying he slipped it into the chamber of his rifle and closed the breech with a snap.

Both Jim and Harry turned away their faces. In a few minutes they knew that they must be prisoners in the enemy's camp. Harry allowed his eyes to travel over the parapet of the fort. He saw the German officers reorganizing their scattered ranks in preparation for a final charge.

And then, from a hill-top towards the south, there came a sound that was like the bursting of a thunder-cloud. Something shrieked and hooted in the air, and a great shell from a heavy gun burst in a flash of flame in the midst of the German troops.

CHAPTER XXII-The Conquest of a Colony

Slowly the guide lowered his rifle. All eyes turned to the south, from which direction had come the shell. For a moment, in the valley, in the enclosure of the fort, there reigned a death-like silence-the silence of suspense. The bombardment of the fort ceased as at a stroke.

The calm voice of Fernando broke upon the stillness.

"The British!" said he. "The soldiers from the Coast!"

Hardly were the words from his lips than a great salvo of cannon thundered in the valley, and went echoing far above the tree-tops of the forests, over the ridges of the mountains, towards Maziriland.

And once again, though the little fort was left in peace, the air was alive with shells, which flew upon their way, shrieking and hooting as if in savage glee. Shrapnel burst high overhead, with white puffs of smoke, the bullets falling like hail into the ranks of the astonished Germans. Segment-shells struck the rocks, breaking into fragments that flew far and wide, inflicting the most terrible of wounds.

The German troops, in good order, shepherded by their officers, retired down the hill, to face this new and far more formidable danger. They assembled on a long spur that jutted into the valley, which they deemed the most suitable position whence to oppose the advance of the British.

"Is this true?" cried Harry. "Is it, indeed, the English?"

"Look!" cried Jim, pointing over the parapet.

A long line of glittering bayonets appeared upon the sky-line, advancing like a running wave upon a low-lying, sandy beach. They came forward without checking, each man keeping his distance from his neighbour, as though they did no more than execute some simple movements on parade. They were in far more extended order than the Germans.

Even as the khaki lines advanced, the Mauser rifles spoke from the hills, and the white dust caused by the bullets flew at their feet. They answered back in volleys, each one of which sounded like the "rip" of tearing paper. The sunshine glittered on the steel of their bayonets, their polished buttons, and the badges on their coats.

Their manoeuvres were like clockwork. When one party advanced, another fired; and thus the long lines of infantry were ever firing, ever advancing upon the enemy's position.

A battle fought under such conditions-which are rare enough in these days when the spade has become an even more important weapon than the rifle-is one of the most magnificent and impressive sights it is possible to see. One catches only glimpses, now and again, of fleeting, crouching figures, running from rock to rock, from cover to cover, appearing and disappearing like gnats in the light of the sun. And all the time a great roar of musketry rises to the heavens-a kind of interminable "crackling" sound, like that of green wood upon a fire, only a thousand times greater in volume and more continuous.

Above this the guns toll ceaselessly, shaking, as it seems, the very ground itself with a series of sullen "thuds", filling the atmosphere with great vibrations, drum-like echoes, and rolling clouds of smoke.

Jim Braid and Harry Urquhart stood side by side upon the parapet of the ancient, crumbling fort. As the gods of Olympus reviewed the struggles of the Greeks and the Trojans, so those two looked down upon the wide amphitheatre where the conflict was taking place, where men were marching shoulder to shoulder into the very jaws of death.

They could see both sides at once. They could see the Germans on the ridge, firing rapidly into the advancing British troops; they could see the British coming on and on, regardless of danger, heeding only the words of command shouted from line to line.

Far in rear, upon a hill-top, a heliograph blinked and flickered in the sun. There was the officer in command. Thence, by means of his signallers, he controlled the army at his feet, disposing his battalions as a player moves his chessmen on a board.

The two boys stood transfixed in bewilderment and admiration.

"Oh," cried Jim, "what wouldn't I give to be there!"

His heart was with his own countrymen, the thin, khaki lines that were driving straight forward with the tenacity of a pack of hounds that hold the fox in view.

From either side gun after gun spoke in quick succession, until it was as if the world was only thunder and flashes of fire and clouds of yellow smoke. As often as each gun was fired it was loaded and fired again. The noise of the batteries was as persistent as the barking of a chained, infuriated dog.

And then from everywhere, from out of the grass, from behind the rocks, from little undulations in the ground, arose thousands of small khaki figures.

Their ranks were undisturbed; they were even as the staves upon a sheet of music. Line after line extended from one side of the valley to the other, and, in the rear of all, the helio still blinked and glittered, there where the brains of the machine were working the destruction of prophets of "Frightfulness", champions of World Dominion.

A bugle sounded in the air, its thin, piercing notes carrying far. Each of the boys experienced a thrill of pride and exultation, a sensation of sublime excitement, as the British lines answered the bugle with a charge.

Line after line, amid the thunder of the guns, swept up the ridge towards the enemy, the bayonets flashing, the bugle speaking again and again.

And then came a cheer that rent the air-a British cheer-howbeit from the throats of gallant Haussas-that drowned the musketry, that rose superior even to the constant growling of the guns.

Before that mad, headlong onslaught the enemy gave way. The Germans were swamped, as a tide carries away a castle on the sands. As one man, they broke and fled, panic-stricken and defeated.

CHAPTER XXIII-Attacked

As soon as they had collected their belongings and stores, they set about to leave the fort, passing through the tunnel in single file, the guide leading the way and Harry Urquhart bringing up the rear.

By the time they entered the forest the afternoon was well advanced, the sun sinking in the heavens. They hoped to reach the British camp that night, but there was no question that darkness would overtake them long before they could do so.

There was little or nothing to fear. The soldiers had driven the Germans from the district. To all intents and purposes the German Cameroons was conquered, and the remnants of the enemy were returning in hot haste towards the Spanish territory to the east.

When Harry Urquhart and his three companions came forth from the entrance to the tunnel they found a heap of hot, charred wood upon the ground. There was no doubt that recently a fire had been burning, and that the picket that guarded the tunnel had retreated only at the eleventh hour.

During the earlier part of the night they traversed the valley, marching in a bee-line towards the bivouac fires of the British camp. They moved forward in the following order-Fernando went first, some distance behind him came Jim Braid and Peter Klein, and a greater distance in the rear was Harry Urquhart.

Harry had been walking for some time with his eyes fixed upon the ground. He was wondering what the end of all this strange business was to be.

He knew that von Hardenberg had stolen the Sunstone, that he carried it upon his person. It was Harry's ambition, the very lodestone of his life, to recover the Sunstone for his uncle. It was von Hardenberg's object to reach the Caves of Zoroaster, and possess himself of the treasure. This was the man's only aim, for which he had proved that he was prepared to sacrifice his country and his honour.

As he walked, Harry was thinking of these things, when, on a sudden, there came a flash of fire, not ten paces to the right. He pulled up with a jerk, and heard a bullet sing past his head like some evil spirit in the darkness. Then there came a stinging sensation in the lobe of an ear, and a moment later he felt the warm blood flowing down his neck.

He saw a figure flying in the night, and with a loud cry took up the pursuit. A few seconds later he had flung himself upon a man who struggled in his grasp. On the instant each seized the other by the throat, and in the moonlight Harry recognized that he had come to death-grips with his cousin, Captain von Hardenberg himself.

No sooner was he aware who his opponent was than he saw at once that here was a chance to capture the Sunstone, and for that end he struggled with the desperation that means more than strength.

Placing one leg behind his adversary, and pressing with all his force upon his chest, he endeavoured to throw von Hardenberg backward. And even as he wrestled he felt the Sunstone, sewn in the lining of the Prussian's coat.

Gradually von Hardenberg was forced backward, and then at last he fell, coming heavily to the ground. In his fall he struck his head against a rock, and after that he lay quite motionless and silent.

Harry could hear the footsteps of approaching men. On one hand Jim Braid and Fernando hastened to the boy's assistance; on the other, the Black Dog came forward with rapidity.

As quick as thought Harry pulled out his pocketknife. He had but to rip open von Hardenberg's coat and the Sunstone was his, their journey was at an end.

A sharp cut with the knife, a hand that trembled with excitement thrust through the opening, and Harry's fingers closed upon the precious relic he had come so many miles to gain.

And, at that moment, a violent blow descended upon his head and stretched him senseless on the ground. The Arab sheikh had come to the assistance of his employer in the nick of time. His quick eyes had taken in the situation at a glance. He had seen the Sunstone in the hands of Harry Urquhart, and, lifting his rifle by the barrel, he had brought down the butt upon the boy's head.

For him to snatch up the Sunstone was the work of an instant. And a moment afterwards the Black Dog was flying in the night, carrying in his arms the unconscious body of von Hardenberg.