I looked at him, stunned by surprise. He noticed my abject astonishment. "I'll go farther," he went on. "Does this discovery of yours concern aircraft; is it designed to bring disaster upon Zeppelins; and are you engaged in perfecting a secret invention in which you have the most entire confidence? In other words, have you nearly perfected a method by which you will be able to successfully combat enemy airships in the air? Tell me the truth, Mr Munro--in strictest secrecy, remember." His words staggered me. How could he know the secret that we had so closely guarded? I did not reply for several moments. "Well?" he asked, repeating his question. "I don't see why I should reveal to anyone--even to you--what I have been doing in the interests of the defence of our country," I protested. "Except that by doing so we should both be able to carry our investigations farther--and, I hope, to a satisfactory issue." I had given my word to Teddy and to Roseye, and they had given their words to me, to disclose nothing. This I recollected and, therefore, I hesitated. The captain, seeing my reluctance, said: "In this inquiry we ought, surely, to assist each other, Mr Munro! Miss Lethmere is missing, and it is for us to unite in our efforts to elucidate the mystery." "But how can answers to the questions you have put to me serve, in any way whatever, to bring us nearer to the truth of what has happened to Miss Lethmere?" I queried. "They do. I merely ask you, yes or no. Your reply will at once place us in a far better position to conduct this most important inquiry," he said. "I may tell you that at present the gravest suspicion rests upon Miss Lethmere." "Suspicion!" I echoed angrily. "Of what, pray?" The captain drew a long breath and, once more looking me straight in the face, replied: "Well, of being a secret agent of the German Government--or to put it very bluntly, of being a spy!" "Roseye a spy!" I shouted, starting up from my chair. "A most foul and abominable lie! How dare you cast any such imputation upon her?" "It is, unfortunately, no imputation, Mr Munro," replied the captain. "You naturally doubt the truth, but we have documentary evidence that the missing lady is not exactly the purely patriotic young person whom you have so long believed her to be. Since the war lots of men who have trusted pretty women have had many rude awakenings, I assure you." "I'll believe nothing against Roseye!" "Well," answered Pollock, taking from his pocket an official envelope, "perhaps you will look at this!" and from the envelope he took a half sheet of dark-blue notepaper of a type and size used by ladies, and handed it across to me, saying: "This was found in her card-case here. From Scotland Yard they sent it over to us this afternoon, and its real import we very quickly discovered."