WHEN the news of what had happened at midnight in the palm grove was published the next morning far and wide through the valley of Aeria it would have been impossible to imagine that an irrevocable sentence of death was overhanging the land and all its inhabitants, save those who were to be selected to take the one chance that remained of surviving the chaos that was to come.

There was no one in the valley to whom Alan’s story was not familiar in all its details, there was not a single heart that had not in the midst of its own happiness sympathised with him and Alma in their sorrow, and so, when that sorrow was at last turned into joy, everyone forgot for the moment the fate whose approach was so near and so certain, and rejoiced with them in the happiness that was great enough to raise them above the gloom that was already stealing over the world.

But in the midst of the general rejoicing came the decision of the Council upon the request which Alan had submitted to his father, and this, though he was forced to confess it wise and just, was by no means what, in his enthusiasm, he could have wished. The rulers of Aeria absolutely refused to permit any of the air-ships to leave the valley for at least two months to come.

They recognised with perfect approval the nobility of the resolve which Alan had taken to carry the message of the world’s approaching end to those nations which he had been, partially at least, responsible for plunging into the horrors of war, but they insisted that the concerns of Aeria must, in their eyes, take precedence of those of the outside world.

There was much to do, and the time for doing it was short. What was perhaps the greatest engineering task in the history of the world had to be conceived and completed within the next four months, and as Alan and Alexis were admittedly the two most skilful practical engineers in the State, the Council declined to allow them to run the almost certain risk of death at the hands of their enemies when their knowledge and skill ought to be devoted to the work of ensuring, as far as possible, the preservation of that remnant of the human race who should be destined to seek safety in the caverns of Mount Austral.

When the completion of that work was made certain, then permission would be freely given to them and their companions to go forth and proclaim their warning to the world, subject only to the condition that they were to take every precaution consistent with the honour of their race to return while there was yet time for them to take their places among the Children of Deliverance should the selection fall upon them.

Meanwhile, telephonic messages were to be sent to all those portions of the world with which Aeria was still in communication, conveying the exact terms of the warning that had been received from Mars, and calling upon the astronomers in all the observatories on the globe to verify the calculations for themselves, and publish their conclusions to their respective nations as quickly as possible.

With these terms Alan was of necessity obliged to be content. Indeed, when he came to review them in sober thought, he saw that, while nothing was to be lost, much was to be gained by submission to them.

Though he still refused, even in spite of the knowledge that he would share with Alma the future if there was to be one, to obey the order of the Council which exempted him from the ordeal of selection, he thought and worked with just as much ardour as though the safety of the whole of the dwellers in Aeria, as well as his own, hung upon his efforts.

The caverns of Mount Austral, like those of other limestone formations in various parts of the world, had been formed in some remote geological period by the solvent action of water charged with carbonic gas upon the limestone rocks.

The entrance to them, discovered very soon after the valley had been colonised by the Terrorists in the first decade of the twentieth century, was situated on the inner slopes of the mountain about eight hundred feet above the level of the lake, which occupied the central portion of the valley.

This lake, although fed by hundreds of streams from the surrounding mountains, always preserved the same level, in spite of the fact that it had no visible outlet. Those who first explored the caverns found the explanation of this phenomenon.

Below the floors of the vast chambers which penetrated the heart of the mountain for a distance of nearly three miles there ran a deep chasm, through which rushed in a black, swift, silent stream the surplus waters of the lake. This stream was nearly a thousand feet below the entrance to the caverns and half that distance below the floor of the lowest chambers and galleries.

The scheme conceived by Alan and Alexis and their fellow-workers was in fact nothing less than the damming of this subterranean stream by a mighty sluice-gate composed of one huge sheet of metal which, running down into grooves cut in the solid rock and metal-sheathed, should completely close the inner mouth of the tunnel by which the waters entered the caverns.

This, once successfully fixed in its place, would deprive the lake of its only known outlet. The streams would go on flowing from the mountains and the waters of the lake would rise. The upper entrance would, when the fatal moment came, also be closed, not by one such door, but by three that would slide down one behind the other in the upper tunnel, which, with a diameter of about thirty feet and a height of almost fifty, ran for nearly a quarter of a mile from the side of the mountain to the first of the chambers.

The spaces between these doors would be filled with ice artificially frozen, and shafts to allow for expansion should the ice melt and the water boil would run from them vertically, piercing the mountain-side. When the waters rose to the level of the entrance the doors would be lowered and the space filled with water and frozen. Then the waters would go on rising, the entrance would be submerged, and the defences of the fortress in which the remnant of humanity was to make its last stand for life would be complete.

But in addition to these outer defences there was an enormous amount of work to be done in fitting the interior of the caverns to receive those for whom they were to form an asylum.

They were already lighted by myriads of electric lamps, but the source of light was outside, and this had to be replaced by power-stations inside. Provision had to be made for keeping the air pure and vital, for supplying food and drink for an almost indefinite time, and for storing up a sufficiency of seeds and roots and treasures of art and creative skill, so that the new world might be clothed again with verdure and nothing essential of the splendid civilisation of Aeria be lost.

Such, in the briefest outline, was the momentous task to which the Aerians devoted all their splendid genius and unconquerable energies, and day by day and week by week they toiled at it, while the fatal hour which was to witness the last agony of man upon earth swiftly drew nearer and nearer.

The messages to the outside world had been sent and replied to. Those to the astronomers and to the governments of the Federation had been acknowledged in formal terms, which thinly concealed the incredulity with which they had been received.

Olga had treated the message with the silent disdain of a conquering autocrat—such, as in sober truth, she now was. The Sultan had replied to it in a despatch in which the dignity of a victorious despot and the fatalism of the religious fanatic were characteristically blended. Then one by one the telephonic communications with the various parts of the world ceased; messages were sent out and repeated, but no answer came back.

First Europe, then Britain, then South Africa, America, and Australia, ceased to respond to the signals; and by the beginning of July Aeria was completely isolated from the rest of the world—probably the only stronghold that now remained unsubdued by the conquering fleets of the Sultan and the Tsarina.

Still the sentinel ships, hanging high in air over the valley, and constantly patrolling the outer slopes of the mountains, saw no sign of hostile approach. The last messages that had been received from the great cities of the Federation had told brief but fearful stories of the desolation that was following in the path of Moslem and Russian conquest.

The bridges of Gibraltar and the Bosphorus had been forced, and thousands after thousands of Moslem troops had been poured into Europe. Frenzied by fanaticism and the new-born lust of battle and conquest, the hordes of Asiatic tribesmen who had escaped the one terrific onslaught of the fleet under the command of Alexis had, now that the guardian ships were withdrawn, been hurried through Russia, and hurled upon the wealthy and almost defenceless cities of Western Europe.

The Federation was on the point of utter collapse, divided in its counsels, confused in its plans of defence, its armies undisciplined, and its fleets disorganised and daily diminishing in number and effectiveness.

In America, Australia, and Southern Africa there was anarchy on earth and terror in the air. Cities had been terrorised into capitulation by aerial squadrons, and then looted and burnt, and their ruins given up to be the miserable prey of the revolutionaries who now, as ever, had taken advantage of the universal panic to revolt against all government, and deny all rights but that which they claimed to prey upon the helpless, all liberty that was not license, and all property that was not plunder.

The last tidings of all that came from Europe were received from Britain, and, after recounting the destruction of London and the collapse of the Government, concluded with the news that Olga had publicly embraced the faith of Islam, and, in conjunction with the Sultan, whom she was to marry as soon as the conquest of Europe was finally complete, was forcibly converting her Russian subjects to the creed of the Koran.

So the affairs of the world stood when the sun went down on the 15th of July. On the meridian of Aeria it set at nine minutes to eight; at thirteen minutes past eight, according to the calculations made by the Martian and verified by the Aerian astronomers, the herald of Fate would approach within the range of terrestrial vision.

Before the brief period of tropical twilight had passed every telescope in the valley was turned to that spot in the constellation of Andromeda at which it was predicted to become visible. As the revolving earth swept Aeria into the shadow of night every light was extinguished, for it was known that the astronomers of Mars would be anxiously watching for a signal that would announce the correctness or the error of their calculations.

Vassilis Cosmo, seated at the eye-piece of the great equatorial telescope on Mount Austral, with his hand on the switch which controlled the electric currents that were waiting to do his bidding, watched the fields of space darken, and the stars of Andromeda shine out. Just a little below the line which joins the Square of Pegasus with the constellation of Cassiopeia, he saw, as usual, the oval, luminous cloud of the great nebula in Andromeda.

Four degrees towards the zenith, above the centre of the star-cloud, a tiny fan-shaped spray, faint and pale as a dissolving puff of white smoke, was floating in the black abyss of space. Precisely at the thirteenth minute of the hour he turned the switch, and the great suns on the mountain-tops blazed out and flashed the signal to the sister-world to tell its inhabitants that their prediction had been fulfilled to the second.