This report was confirmed by the detector which gave the "Vorwartz's"

position as sixty-three miles to the north-west. Captain Restronguet noticed that he was gaining rapidly on his rival, and had been unable to account for the rapid decrease in the intervening distance unless Karl von Harburg had lighted upon an isolated spot that seemed to suit his requirements.

At Kaira Captain Restronguet was able to procure an old though fairly reliable Portuguese map of the course of the river, and on this the position of the rival submarine was carefully noted. If she succeeded in floating and proceeding up the Zampa River it was evident that the "Vorwartz" would soon be in British territory--the colony of Rhodesia.

That same evening a wireless message--the first for three days--was received from Captain Restronguet's English agent stating that the Foreign Office was in communication with the government of the Portuguese Republic, and an arrangement had been arrived at whereby three British sternwheeler gunboats that were used to patrol the Shire River, were to be allowed to descend to the Zambezi and attempt to cut off the "Vorwartz" on her return.

"Evidently the British Navy wants to chip in at the death," commented Captain Restronguet. "We must look to our laurels. It would be hard lines to be searching for days amongst these unexplored backwaters without success, and to find that one of these little paddle-boats by a piece of sheer good luck had managed to blow the 'Vorwartz' to smithereens while she was lying helplessly stranded on a mud-flat."

Hythe did not reply. He was naturally anxious, now that he had been on board the "Aphrodite" for such a lengthy period and had faced perils in company with her crew, that Captain Restronguet should receive a just reward for his strenuous endeavours; yet he did not forget that he was still an officer of the great British Navy, whose policy is to be ready, aye ready, in the hour of triumph or in the hour of disaster alike.

Just then Carnon, who since Kenwyn's illness had been appointed solely for duties in connexion with the detector, approached and saluted.

"The detector, sir, has gone wrong," he reported.

"Gone wrong? What do you mean? Have you been tampering with the instrument?"

"No, sir. The last reading gave sixty-one miles. That was five minutes ago. When I looked again there was no record at all. The batteries are still working: I could get a spark an inch in length. The terminals are properly clamped."

Captain Restronguet, Devoran, and the sub hastened to the compartment in which the detector was fixed. The indicator board was absolutely blank.

"We're not having an easy time of it at all," remarked the captain.

"Without the detector it is quite possible that the 'Vorwartz' may yet outwit us. All the same, I cannot understand it."

"We know her position up to ten minutes or a quarter of an hour ago, sir," said the first officer.

"Quite so, Mr. Devoran; and we must work on that. It will take us three hours, running at the highest speed compatible with prudence in this brute of a river, to arrive at the spot where the 'Vorwartz' was last reported. In three hours Karl von Harburg may have shifted a long distance off--or he may not."

"And there's Kenwyn to be taken into account."

"I haven't forgotten him. I think after all we had better keep him on board. It is too much of an undertaking for two men to have and tend him, provide for themselves, and be on their guard against the wild animals that abound, and a dozen other difficulties that a camp on sh.o.r.e would entail. However, pa.s.s the word for a speed of twenty-four knots.

Allowing for the adverse current we ought to be at the confluence of the Zampa River well before sunset."

Just above the town of Shemba the Zambezi bifurcates, the two streams reuniting twenty miles higher up. It was just possible that the "Vorwartz," bound towards the sea, might be pa.s.sing down one branch while the "Aphrodite" was proceeding up the other; but this time luck was in Captain Restronguet's favour, for above the junction the "Aphrodite" fell in with a trading steamboat, whose captain, by signs, made it clear that no vessel of any description approaching the "Vorwartz" had pa.s.sed down the left-hand stream.

The river here was considerably narrower and deeper than nearer its mouth. Its width was still over half a mile, while the soundings gave a level bed of six fathoms. Here, also, the tide was no longer felt; but, owing to a cessation in the rainfall, the level of the river was gradually sinking.

During the course of the day several canoes pa.s.sed at a respectful distance; but late in the afternoon a craft of some sort was sighted drifting down in mid-stream.

As the "Aphrodite" approached it was seen that the object was a raft composed of several slender spars supported by four barrels, to which were lashed four or five short planks. Lying on the platform thus formed were two human bodies.

"What do you make of it, Mr. Devoran?" asked Captain Restronguet. "A tragedy--not exactly on the high seas--but one of a very extraordinary nature. They look like Europeans."

"Shall I have the boat lowered to investigate, sir?"

"No, they're dead right enough. I've been watching them pretty carefully through my gla.s.s for some time. If it's a case of contagious disease we had better sheer off."

"Why, they're Chinese!" exclaimed Hythe.

"Chinese? Then they must be some of the crew of the 'Vorwartz'," said Captain Restronguet. "Evidently von Harburg has met with disaster."

As the submarine pa.s.sed the aimlessly drifting raft a fairly close view could be obtained of the dead Chinamen. They were dressed in blue cotton suits after the style affected by Chinese seamen serving in European vessels, but there was no mistaking the Tartar features and the slanting eyes. That they were stone dead there could be no doubt, for there were several birds hovering around the raft in a manner that their natural timidity would not permit if the two bodies showed signs of life.

"Do you think that a catastrophe has occurred to the 'Vorwartz,' sir, or were these men merely attempting to escape?" asked the sub.

"Coupled with the fact that our detector has failed to give any indication of the 'Vorwartz,' I am inclined to favour the first theory,"

replied Captain Restronguet. "Since our apparatus is, as far as I can tell by careful examination, in perfect working order, I can only put its unresponsiveness down to the failure of the electric current on board the 'Vorwartz.' That, of course, would account for the failure of our detector."

"And the 'Vorwartz' could otherwise be capable of action?"

"To a certain extent. But without electricity she can have no means of compulsion, no means of offence, unless we except the use of fire-arms.

However, before to-morrow is past we ought to discover her whereabouts.

I am not proceeding further to-day as night is approaching. As soon as we find a suitable depth we'll descend till morning."

Another night pa.s.sed without interruption. The detector was still silent, but the "Aphrodite" was now within a few miles of the spot where the "Vorwartz" had last given notice of her presence.

It was not a desirable day. Torrential rains were falling, while the atmosphere was too close to wear oilskins without the greatest discomfort. Consequently on the "Aphrodite" rising to the surface her crew save three had to remain below.

Captain Restronguet, Hythe, and Carclew were in the for'ard conning-tower, Devoran, Carnon the quartermaster, and Polglaze occupied the after conning-tower, so as to maintain a careful look out on all sides. Three men, braving the heavy downpour, were stationed for'ard, where they took turns in casting the lead.

The river here was considerably narrower--about thrice the width of the Thames at London Bridge. The banks on either hand were low and densely covered with thick scrub and extensive forests of tropical trees; while the skyline was broken on both sides by serrated ridges of lofty mountains.

"This must be the Zampa River," said Captain Restronguet, pointing to a fairly wide waterway that joined the Zambezi on its right bank. "Here the 'Vorwartz' was sighted by the natives. It would be well to explore the stream before going further."

"It looks too shallow to take anything more than a flat-bottomed light-draught vessel," remarked Hythe. "Still, as you say, sir, we ought to leave nothing unexplored behind us. If you wish I will take charge of the whaler and see what it is like."

"Very good, Mr. Hythe. I shall be obliged if you will. We'll remain here. Do not proceed further than there is depth for the 'Aphrodite' to follow. Should you require a.s.sistance fire three explosive rockets. If anything should necessitate your immediate return I will make a similar signal. Should you locate the 'Vorwartz,' endeavour to return without being seen."

It certainly required plenty of zeal to volunteer for a boating expedition on a tropical river in such torrential rains, but the men called upon for the service responded with alacrity.

Four rowers stripped to the waist sat on the thwarts, apparently quite indifferent to the rain. Hythe, Polglaze, and Carclew were in the stern sheets, partially protected by an awning, but before the whaler pushed off the canvas covering, sagging under the quant.i.ty of rain water, was found to be of more trouble than use, for a regular stream poured through the canopy upon the sub's head and shoulders. Since it was also likely to attract the attention of Karl von Harburg's men Hythe ordered it to be struck, and accepting the situation as well as he could, was soon soaked to the skin.

The tributary was found to be nearly twenty feet deep towards the right-hand bank. On both sides were belts of malodorous mud on which numerous crocodiles were lying as if enjoying the rain. Others, looking more like floating logs, were drifting in the channel, and careful steering was needed to avoid them. Hythe realized that he was not on a sporting expedition, and should any of the saurians become infuriated it would be necessary to fire at the reptile. The report of the rifle would give the alarm to the "Vorwartz" should she be within hearing, and the chances of locating her without being discovered would be very remote.

For more than a mile the rowers toiled manfully. The current was strong, the boat heavy, while Polglaze had to bale incessantly to prevent the rain from rising over the stern gratings. The "Aphrodite"

was now lost to view by an intervening bend in the course of the stream.

The depth still continued regular, and afforded plenty of water for a craft like the "Vorwartz" to ascend if her ballast tanks were emptied, but as reach after reach was opened out no sign of the rival submarine was visible--only a monotonous stretch of coffee-coloured water enclosed on either hand by the soft stagnant mud that effectually prevented any attempt at landing.

"What's that, sir?" asked Polglaze, suddenly holding up his hand and listening attentively.

"Lay on your oars, men," ordered the sub.

Above the hissing of the rain Hythe could distinguish the deep purr of a powerful motor. Could it be that the "Vorwartz" was returning? If so, escape was impossible, for no cover of any sort was obtainable, and long before the whaler could return to the "Aphrodite" she would be overtaken by the swiftly moving submarine.

"It's that brute of a von Harburg coming downstream, sir," exclaimed Carclew. "We're fairly trapped."

In reply the sub ordered the boat to be turned and her head pointed down stream. Drawing the three detonating rockets from a locker under the stern sheets he rapidly lashed the sticks in position. Happen what may the "Aphrodite" must have warning of her enemy's approach. Perhaps, as the "Vorwartz" was now under way her electrical current would operate the detector onboard the "Aphrodite"; if so there was every reason to suppose that Captain Restronguet was already on his way to rescue his whaler's crew and engage his sworn foe. A chance of safety yet remained.

"Give way, men," ordered Hythe. "We may do it yet."