"Why I ask," continued Sir John Pilrig, "is this: here is a portion of the report of the officer commanding H.M.S. _Basilikon_. He lays particular stress upon the fact that when two of our seaplanes were about to attack one of the Rioguayan cruisers, they were unable to approach within two miles of her. They simply had to descend through ignition troubles, but on the hostile vessel increasing her distance the defect--if defect it could be termed--was no longer in evidence. That phenomenon occurred on three occasions during that operation." Peter threw a sidelong glance at his uncle. Brian's face was pale beneath its tan. "By Jove, Peter!" he exclaimed. "Ramon Diaz has got to wind'ard of us. He's stolen the plans of the rays." "Explain, please," said the Deputy Chief of Staff. In answer, Brian Strong stopped and undid the fastenings of a leather portmanteau which, like the haversack, he had so carefully guarded in his flight from El Toro. From it he drew a complicated "valve set" and placed it upon the table. "This, sir," he replied, "is the secret. I had hoped that it was a secret still, but your information unfortunately leads me to think otherwise. With an apparatus embodying this invention, I can truthfully claim to bring down any aircraft in existence. It was my intention to give my secret to the British Government, and it is for that purpose that I am here. Unfortunately, it is a secret no longer. By some means, the Rioguayan Government has acquired the knowledge and has already put it to practical use." Briefly, Brian Strong explained the device, giving particulars of the experimental flight in which Peter had taken a practical part. "It is, of course, unfortunate," admitted Sir John. "But tell me, in the event of two opposing forces using a similar device, would the rays of one affect the other?" "Undoubtedly," affirmed Brian decidedly. "Well, then," continued the Deputy Chief of Staff, "the position, I take it, would be this: the aircraft of both opponents would be rendered ineffectual. That's something. It leaves the conduct of operations in the hands of other branches of warfare. In the present instance--warships." "Precisely," agreed Brian. Sir John went to the window and gazed across the Mall, apparently deep in thought. Suddenly he turned to his visitor. "If you had an up-to-date workshop and a staff of highly-trained mechanics at your disposal, Mr. Strong, how long would it take you to produce a complete apparatus for testing purposes?" "Two days," replied Brian, without hesitation. "Excellent," exclaimed Sir John, touching an electric bell. "I will make arrangements for you to proceed to the naval gunnery establishment at Whale Island, where all facilities will be provided. There is one other matter. I trust you will not mind my mentioning it--the question of funds." "That's all right, Sir John," said Brian. "I can carry on without--er--financial assistance for a bit. When the gadget's proved----"