Chris sprang, slashing the butt of the gun downwards. The lead was false. He hurtled jarringly into the door jamb, the gun thumping against the floor. The wind was knocked from him; the nausea of his wound swept him again with a surge of dizziness. But the painful scuffle of unseen feet ahead pulled him up once more; like a punch-drunk fighter he staggered out from the cubby to the ladder and hauled himself up the steps. He half-fell at the top, but his mind was clearing; and as he swayed there he knew what he had to do--saw the duty that lay before him.... More slowly, he crawled after the dragging footsteps and the gasps of the invisible raider, following them through the vast dimness of the interior of the dirigible ZX-1. * * * * * The chief operator on duty in the flagship of the Black Fleet swung round in his seat and yelled through into the bridge of the massive battleship: "Urgent, sir! From the ZX-1!" A moment later the captain of the ship, for the fleet's admiral was out in a launch inspecting what little of the fallen ZX-2 was still floating on the surface, was at the operator's side, listening amazedly. The operator read off, word for word, what Chris Travers had sent. "... There was a contrivance planted aboard to blow up the ship and send it down in flames as the ZX-2 was. The thing that did it is--" he finished, and fell silent on that uncompleted sentence. The captain's lined face expressed incredulity. "My God!" he burst out. "First the ZX-2, now-- That all?" "Yes, sir. I can't get any answer or connection." They stared at each other. Finally the captain spluttered: "Is some maniac loose in this fleet? Don't sit there like a fool, man! Get in touch with the _Saratoga_; tell 'em what you received; tell 'em to send some men up to that dirigible, wherever she is. We can't lose both of them!" The operator's fingers skipped nimbly; even while he was speaking into the microphone, the red-faced captain had rushed back into the control bridge and was roaring: "Signal the Admiral back here! Hurry!" * * * * * Things moved quickly then; small things, but significant. A casual eye glancing over the ranks of the Black Fleet as it lay around the scene of the tragedy, waiting for orders, would not have noticed any difference. The launch containing the fleet's admiral, which had been fussing about with its load of officers and various dignitaries, suddenly wheeled and pointed back for the mammoth flagship, in response to swift signals from the arms of a gob on her bridge; and, on the broad landing deck of the carrier, _Saratoga_, two three-seater planes, equipped with automatic clamps for a dirigible's rack, were wheeled up to the line. Their props were spun over. But even before their cockpits had been filled, an officer on the bridge of the flagship, and a dozen others throughout the fleet, cried: "There she is!"