This he pointed out to Ella, who, in reply, said: "Yes. I shall remain here and watch. I shall close up my flat, and send my maid on a holiday, so as to have excuse to remain here at home." "Right-ho! darling. You can always get at me on the telephone. You remain here and watch at this end, while I will keep an eye on Ortmann-- at least, as far as my flying duties will allow me." Thus it was arranged, and the pair, treading noiselessly, closed the door and, relocking it, crept softly down the stairs. In the dark hall Seymour took his well-beloved in his strong arms and there held her, kissing her passionately upon the brow. Then he whispered: "Good-night, my darling. Be careful that you are not detected watching." A moment later he had slipped out of the door and was gone. Hardly had the door closed when Ella was startled by a movement on the landing at the head of the stairs--a sound like a footstep. There was a loose board there, and it had creaked! Some one was moving. "Who's there?" she asked in apprehension. There was no reply. "Some one is up there," she cried. "Who is it?" Yet again there was no response. In the house there was the old servant and her father. Much puzzled at the noise, which she had heard quite distinctly, she crept back up the dark stairs and, finding no one, softly entered her father's room, to discover him asleep and breathing heavily. Then she ascended to the servant's room, but old Mrs Pennington was asleep. When she regained her own cosy room, which was, as always, in readiness for her, even though she now usually lived in the flat in Stamfordham Mansions, over in Kensington, she stood before the long mirror and realised how pale she was. That movement in the darkness had unnerved her. Some person had most certainly trodden upon that loose board, which she and her lover had been so careful to avoid. "I wonder!" she whispered to herself. "Can there have been somebody watching us?" If that were so, then her father and the chief of spies, the man Ortmann, would be on their guard. So, in order to satisfy herself, she took her electric torch and made a complete examination of the house, until she came to the small back sitting-room on the ground floor. There she found the blind drawn up and the window open. The discovery startled her. The person, whoever it could have been, must have slipped past her in the darkness and, descending the stairs, escaped by the way that entrance had been gained. Was it a burglar? Was it some one desirous of knowing the secrets of that upstairs laboratory? Or was it some person set to watch her movements? She switched on the electric light, which revealed that the room was a small one, with well-filled bookshelves and a roll-top writing-table set against the open window. Upon the carpet something glistened, and, stooping, she picked it up. It was a woman's curb chain-bracelet, the thin safety-chain of which was broken.