"Hope we haven't kept you waiting, Brett," Hewitt said. "This is Mr. Bell, of Kingsley, Bell and Dalton; it took me a little longer than I expected to reach him. His offices are shut, and the clerks all gone, but we are going to turn up the lights for a bit. The lift man is gone too, I expect, so we shall have a good long stair-climb." As to the lift man Hewitt was right, and during our long climb I received, briefly, an account of the loss Mr. Bell's firm had suffered. "I have told Mr. Bell," Hewitt said, "that it was you who happened across the key in such an odd fashion, and when I wired I was sure he would be glad to let you see the upshot of your strange bit of luck. I was also pretty sure that you would like to see it, too. For I really believe that this case--which I confess seemed pretty near hopeless a few hours ago--is coming to an issue now, and here." "Did you get any information out of the man in the hospital?" I asked. "Not a scrap," Hewitt replied. "He was still insensible, and though I saw his clothes, and they told me a good deal about the gentleman's personal habits--which are not dazzlingly noble, to put it mildly--they told me nothing else whatever, except that he had recently been knocked down in the mud, which I knew already. But the cypher has told me something, as I will explain presently." By this time we had reached the high floor in which the offices stood, and Mr. Bell, all wonder and pale agitation, unlocked the outer door, and turned on the electric light. "Now," cried Hewitt, "show me your ventilators!" There were some, it seemed, in the top panes of the windows, but these were not what Hewitt wanted. There were others in the form of upright chambers or flues, made of metal, and painted the same colour as the walls about them. They rose from the floor in corners and wall angles, and could be shut or opened by means of lids over their upper ends. These were more to Hewitt's mind, and he went about from one to another, groping under the lids, and poking down into the flues with a walking-stick. There was a wire-grating, or diaphragm, it seemed, in each of them, two or three feet down, and we could hear the end of the stick raking on this at each investigation. One after another of these ventilators Hewitt examined, till he had examined them all, in outer and inner rooms, without result; and I could see that he was disappointed. "There must be another somewhere," he said, and hunted afresh. But plainly he had tried them all, and now he could do no more than try them all again, with as little result. "It _is_ a ventilator," he said, positively. "Unless----" he broke off thoughtfully and stood silent for a few moments. "Ah! of course!" he resumed presently. "We'll send for the housekeeper and a candle. Which is the nearest empty office--the nearest office to let? Is there one on this floor?"