The other letter was from Tremayne, dated more than a fortnight previously, and gave him a brief _résumé_ of the course of events in Europe since his voyage of exploration had begun. It also urged him to push on the construction of the aërial navy as fast as possible, as there was now no telling where or how soon its presence might be required to determine the issue of the world-war, the first skirmishes of which had already taken place in Eastern Europe. Natas and the Chief were both in London, making the final arrangements for the direction of the various diplomatic and military agents of the Brotherhood throughout Europe. From London they were to go to Alanmere, where they would remain until all arrangements were completed. As soon as the fleet was built and the crews and commanders of the air-ships had thoroughly learned their duties, the flagship was to go to Plymouth, where the _Lurline_ would be lying. The news of her arrival would be telegraphed to Alanmere, and Natas and Tremayne would at once come south and put to sea in her. The air-ship was to wait for them at a point two hundred miles due south-west of the Land's End, and pick them up. The yacht was then to be sunk, and the Executive of the Terrorists would for the time being vanish from the sight of men. It is unnecessary to say that Arnold carried out the plans laid down in this letter in every detail, and with the utmost possible expedition. The _Avondale_ arrived the next day at the island which had been chosen as a dockyard, and the ship-building was at once commenced. All the material for constructing the air-ships had been brought out completely finished as far as each individual part was concerned, and so there was nothing to do but to put them together. The crew and passengers of the steamer included the members of the Executive of the Inner Circle, and sixty picked members of the Outer Circle, chiefly mechanics and sailors, destined to be first the builders and then the crews of the new vessels. These, under Arnold's direction, worked almost day and night at the task before them. Three of the air-ships were put together at a time, twenty men working at each, and within a month from the time that the _Avondale_ discharged her cargo, the twelve new vessels were ready to take the air. They were all built on the same plan as the _Ariel_, and eleven of them were practically identical with her as regards size and speed; but the twelfth, the flagship of the aërial fleet, had been designed by Arnold on a more ambitious scale. This vessel was larger and much more powerful than any of the others. She was a hundred feet long, with a beam of fifteen feet amidships. On her five masts she carried five fan-wheels, capable of raising her vertically to a height of ten thousand feet without the assistance of her air-planes, and her three propellers, each worked by duplex engines, were able to drive her through the air at a speed of two hundred miles an hour in a calm atmosphere.