Happily, however, that big brown deal box had not been there, and I smiled within myself at the bitter disappointment which must have been theirs. In any case, our great secret was still safe. "Well," I said. "You certainly had a most exciting adventure, Theed. We'll have to set a trap for these gentry in future. Just think out something, will you, and Mr Ashton and I will help you. If they come again we might put in a little electric `juice' which will effectively stop them from meddling with our things in future. They might get a very nasty jar," I added, laughing. "But 'ow do you think they got hold of that duplicate key, sir?" asked the grey-haired old pensioner. I hesitated. The whole affair was a most complete mystery, and only went to bear out Teddy's declaration that, on the night of our test, somebody must have been about and expressed sudden surprise at its astounding result. From the telephone call-box inside Hammersmith Broadway station I rang up Teddy at Hendon, and asked him to meet me there after lunch. This he did, and as together we walked away from the hangars, so as not to be overheard, I related to him the strange story, as told by old Theed. He stood astounded. "Somebody knows, my dear Claude! Who _can_ it be?" "Who knows? Only ourselves, Roseye and the Theeds. Nobody else," was my quick reply. Then, suddenly, he said: "I suppose Roseye couldn't have dropped any hint to her father? If so, the latter might have spoken to Eastwell--or somebody else!" "Roseye made to me a solemn promise of secrecy, and I trust her, Teddy," I said very quietly. "So do I, my dear fellow. So do I," he assured me. "Well--I can't fathom the mystery at all. Evidently they were on some desperate errand--or they wouldn't have knocked poor old Theed senseless--eh? And the woman! Who could she have been?" "Who knows?" I asked. "Nevertheless, we must make it our business to find out, my dear chap," I added in earnestness. "We've got secret enemies somewhere--probably around us here. Indeed, that has been my firm conviction for some time." "And mine also. So let us keep open eyes everywhere. Where's Roseye? Is she coming over this afternoon?" "I expect her every minute. She'll be astounded and excited." "You won't tell her--shall you? It will only alarm her, Claude--and I never advocate alarming a woman." I paused. Instantly I realised the weight of such an argument, for Roseye was, after all, a dainty and highly-strung little person, who might worry herself over the mystery far too much. "Yes, Teddy," I said somewhat reluctantly. "I quite agree. At present we'd best leave matters as they are, and keep our own counsel." Hardly were those words out of my mouth when we saw my well-beloved, with face flushed in glad welcome, coming across to us. She had evidently arrived in her car, and already put on her air-kit, for, it being a fine afternoon, she intended to make a flight.