Taking Mostyn Brown's side, I suddenly interjected a sentence in German. Apparently hardly noticing the change in his excitement Mostyn Brown replied in the same language, and his accent told me at once that he was not of British birth. There was no possibility of mistake, for, however well the Hun may speak our tongue, he will inevitably betray himself when in a moment of excitement he lapses into his own language. My suspicions of Mostyn Brown were naturally intensified a hundredfold by this discovery. Of course, I redoubled my efforts, and was in daily conference with certain highly placed people in Whitehall, whose curiosity was now fully roused, as well as with my own agents, the vivacious Madame Gabrielle and the slow, but painstaking and relentless, Aubert. The watch on the suspects became closer than ever, and I was convinced that, try how he might, none of them could move, practically speaking, without full details of what he was doing reaching me in the course of an hour or two at most. And I was ready to strike hard at the earliest moment when decisive action might seem justified. For the moment, however, there was nothing to be done but watch and wait, tense and expectant, while night by night the moon drew nearer and nearer to the full. Thanks to the information I was able to place before the authorities in Whitehall, there was little chance of the anti-aircraft defences of London being caught napping, while the secret signal I had discovered--the changing of the coloured ribbon on the parrot's cage at Mostyn Brown's house in Lembridge Square--would be almost certain to give us warning of any long-arranged raid in force. Apart from the sequel, the worst we had to expect was a sudden dash by a few machines in the event of an unexpected improvement in the weather rendering such a course possible. But with regard to the big raids, involving days of patient preparation, settled weather, and most careful and thorough organisation, we felt tolerably sure that the tell-tale ribbon would give us the warning we wanted. So it proved in the event, and once again the Hun's trickiness brought his carefully planned scheme to failure. CHAPTER THIRTEEN. HOW BERLIN OBTAINS INFORMATION. At last the day--or rather the night--which we had been expecting came. The sun had risen in a cloudless sky, and all day long had poured down a fierce flood of heat and light. London was stifling. Everyone seemed to be the victim of heat lassitude; tempers were decidedly short, and even the most amiable of people seemed suddenly to have developed raw-edged nerves. Added to all this was an uneasy presentiment of danger; "There will be a big raid to-night," was the thought in the back of everyone's mind.