Within a hundred miles of the frontier the two fleets stopped, and Alexis went on board his own vessel. It was then a few minutes after three in the morning, that is to say, about an hour before sunrise, and the warships were floating in a serene and cloudless atmosphere at an elevation of nearly four miles, or about twenty thousand feet. It was already quite light enough at that elevation for signals to be plainly seen, and a rapid interchange of these took place, communicating the final instructions from the flagships to the commanders of the smaller squadrons into which the fleets were to be divided. Just as the last signal had been answered, and the vessels were about to separate, a tiny speck of light was seen far away to the westward. A hundred powerful field-glasses were instantly turned upon it, and soon showed it to be a hostile air-ship coming up very fast at an elevation of about three miles. The silvery sheen of her hull instantly betrayed the fact that she was neither an Aerian nor a Federation vessel, for the former were blue and the latter painted dull grey. A moment’s reflection showed that she must have sighted the Aerian fleet, and if she got past would take tidings of its presence to the frontier and destroy all hope of a surprise. Within twenty seconds of her true nature being made out a signal was flying from the mizzenmast of the _Isma_, which read, “Shall I stop her?” “Yes. Cripple her if you can. Don’t fire unless necessary,” came the reply from the _Avenger_, and the _Isma_ at once darted away on her errand. Alexis, of course, understood that if he struck the enemy with a shell her fragments would fall to the earth, and might probably give the impression that a battle was being fought in the air, and, as they were now so near to the Russian frontier, this was to be avoided if possible. He therefore determined to cripple her without destroying her, and, if he could manage it, to capture her in mid-air, a feat that had never been performed before under similar conditions. He descended until the _Isma_ was only floating about a thousand feet higher than the enemy, and then began to fly round and round in a wide circle, at a speed which made it practically impossible for her to be hit with a shell, save by the merest chance. The stranger, on sighting the fleet, slowed down and swung round to the northward, so as to have the advantage of being able to present her stern chasers to the enemy. This gave Alexis the opportunity he wanted. The instant that her stern was visible, the _Isma_ swooped down, and rushed at her at such a speed that she looked more like a stream of blue light flashing through the sky than a solid material body. Those on board her saw this flash dart past their stern. Their ship shivered from stem to stern with some shock that came so swiftly that not until the _Isma_ was almost out of sight did they realise the damage that had been done. [Illustration: THE “ISMA” SWOOPED DOWN. _Page 281._]