"They will never know that," I declared with entire confidence. "I can tell you both that the secret experiments of Ashton and myself have been crowned with success. We have, however, been most wary and watchful. We are well aware that at our works out at Gunnersbury there have been intruders, but those who have dared to enter at night to try and discover our plans have been entirely misled and, up to the present, no single person beyond ourselves has ever seen, or has ever gained any knowledge whatsoever of that electrical arrangement which constitutes our discovery." "Then you really can fight Zeppelins?" asked Barton, much interested. I nodded in the affirmative, and smiled. "So what is written here in cipher is perfectly correct?" asked Pollock. "Perfectly. The missing lady has actively assisted Mr Ashton and myself in our experiments." "And apparently the lady wrote down this message giving you away," remarked Barton. "Somebody wrote it--but it certainly is not her handwriting." "Quite so. Spies frequently get other persons to copy their messages in order that they can disclaim them," replied the Intelligence officer. "We've had several such cases before us of late." His words aroused my anger bitterly. That Roseye had held any communication with the enemy I absolutely refused to believe. Such suggestion was perfectly monstrous! Yet how was it possible that anyone should know of the success of our experiments at Gunnersbury? Recollection of that well-remembered night when Teddy had declared there had been strangers prowling about, flashed across my mind. I knew, too well, that the evil that had befallen me, as well as the disappearance of my well-beloved, had been the work of the Invisible Hand--that dastardly, baneful influence that had wrecked my machine and nearly hurled me to the grave. "Well," I said at last, "I would much like a copy of this remarkable document." "I fear that I cannot give it to you, Mr Munro," was the captain's slow reply. "At present it is a confidential matter, concerning only the Department, and the person in whose possession it was." "We must find that person," I said resolutely. "What is your theory regarding Miss Lethmere?" I asked, turning to Barton. "Well, Mr Munro, it would appear that either the lady herself, or some thief, threw the chatelaine from a train passing north through the tunnel." "There may have been a struggle," I remarked, "and in trying to raise the alarm it might have dropped from her hand." "That certainly might have been the case," the inspector admitted. An hour later, accompanied by Teddy and Barton, I set out from King's Cross station and, on arrival at Welwyn--a journey a little over twenty miles--we spent the evening in searching inquiry. The station-master knew nothing, except that both tunnels had been searched without result.