After Martin Hewitt had rushed off to St. Augustine’s Hospital with the key, the envelope, and the cypher I had brought him, I heard nothing of him till dusk fell — about six. Then I received this telegram:—

“Cypher read. Most interesting case. If you can spare an hour be outside 120 Broad Street at six thirty. — Hewitt.”

I had to be at my office between eight and nine, and to keep Hewitt’s appointment I should probably have to sacrifice my dinner. But I was particularly curious to know the meaning of that cypher, and just as curious to know how it could be read; and, moreover, I knew that any case that Hewitt called interesting would probably be interesting above the common. So I took my hat and sought a cab.

I was first at the meeting-place — indeed, a little before my time. No. 120 Broad Street was a great new building of offices, most, if not all, closed at this time — a fact indicated by the shutting of one of the halves of the big front door, where a char-woman was sweeping the steps under the board which announced that offices were to be let. I waited nearly a quarter of an hour, and then at last a hansom stopped and deposited Hewitt and another older gentleman before me.

“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?”

“I think not,” Mr. Bell answered. “But there’s one on the floor below, just opposite the lift — I see the bill on the door every day as I come up.”

“We’ll try that, then. I’ll rake out every ventilator in this palatial edifice before I’ll call myself beaten. Come, call the housekeeper. Is there a speaking tube? Tell him to bring a light.”

The housekeeper came, wonderingly, with a watch-man’s oil-lantern, and we all went to the floor below. Opposite the lift was a glass door from which a bill had recently been torn.

“Why, it’s let!” said Mr. Bell.

“Yes, sir,” assented the housekeeper. “Let a day or two ago to a Mr. Catherton Hunt. Or, at least, a deposit was paid.”

“But see — the door’s not locked,” Hewitt observed, pushing it open. “I think we’ll trespass on Mr. Catherton Hunt’s new offices, since they seem quite empty, and he hasn’t taken possession. Come — ventilators!”

It was a small office — an outer room of moderate size, and one smaller inner room. Hewitt at once attacked the ventilators in the larger apartment — there were two of them — but retired disappointed from each. There was one ventilator only in the small room. Hewitt tilted the lid, which was at about the level of his eyes, thrust in his hand, and drew forth a bundle of folded papers; thrust in his hand again and drew forth another bundle; did it again, and drew forth more!

Mr. Bell fell upon the first bundle almost as a dog falls upon a bone; and now he snatched eagerly at each successive paper or bundle, till Hewitt raked the grating with his stick, and declared that there were no more. “Is that all?” he asked.

Mr. Bell went tremblingly from paper to paper, and, at last, said that he believed it really was. “I can verify it by the list upstairs,” he added, “if you are sure there are no more.”

“No more,” repeated Hewitt, rattling his stick in the ventilator again. “Let us go and verify, by all means.”

We sent the puzzled housekeeper away, and returned to the office above, and presently Mr. Bell, now beginning so far to recover from his amazement as to express incoherent gratitude, reported that the bonds were correct and complete to the last and least.

“Very well,” said Hewitt, “then my part of the business is done, though I must say I’ve had luck, or rather, Brett has had it for me. But the police must come on now. I think, Mr. Bell, we’ll go along to Scotland Yard when we leave here. They’ll be wanting to see Mr. Catherton Hunt, I expect, whoever he is — and somebody in your office, too, if I’m not sadly mistaken.”

“Who?” gasped Mr. Bell.

“That, perhaps, you can help to point out. See here — do you know whose figures they are?” and Hewitt produced the small slip of paper containing the cypher.

“They’re very small,” remarked Mr. Bell, putting on his glasses; “very small indeed; but I think — why they’re Henning’s, I do believe!”

“Ah! one or two other little things seemed to point that way. Henning is your correspondence clerk, I believe, and I expect this thin little slip is a specimen of your typewriter paper. Have you any of his written figures for comparison?”

“Well no — I hardly think — you see he typewrites his letters, and although I know his writing very well I can’t at the moment put my hand on any figures of his.”

“Never mind — it’s mere matter of curiosity; the police will ask him questions in the morning. What I believe has happened is this. Our friend Henning — if he’s the man — has a friend outside a great deal cleverer than himself — though he would seem to have his share of cunning, too. Between them they resolved to rob you in the way they have done — temporarily. Henning was to take............