"Yes, Mr. Foster," Hewitt added pleasantly, "I'm not sure that the lock is quite in order, but I promised to open it for Mr. Bell, so we'll try."

Mr. Foster, a slim, active old gentleman, grown grey in the firm's service, pulled a bunch of keys from his pocket, and Hewitt scrutinised each narrowly. "No," he said, "I'm afraid none of these will do. Stay," he added suddenly, and turning his back, carried the bunch to the window. "No," he concluded, as he came back to the table and tried one of the keys fruitlessly. "No, I'm afraid none of those will do. Thank you, Mr. Foster. You don't happen to have any more, do you?"

No, Mr. Foster hadn't any more, and he retired to his room. Then Mr. Bell called the correspondence clerk, Mr. Henning. Mr. Henning was a much younger man than the head clerk-twenty-six or so-pale and blue-eyed, with weak whiskers and a straggling moustache. His keys were just as readily produced as Mr. Foster's, but again Hewitt's examination was unsuccessful. The only other key he had belonged to the typewriter, and that did not fit.

Then came Mr. Potter, the book-keeper, round, and tubby, and puffy, and his keys went under inspection in the same way, taking a little longer this time, with two separate dashes to the light of the window. Then there was Mr. Robson, young and spruce, Mr. Clancy, older and less tidy, and four or five more. All the keys were examined, all with the same lack of success, and all the clerks were sent away to take their turns at lunch.

"No," Hewitt reported, as soon as he and Mr. Bell were alone again, "it was certainly none of those keys. Though indeed, my little attempt was desperate at best. A man would be a fool to keep that key longer than he needed it, and especially to string it with his others. Still, of course, it is by just such blunders as that that nine criminals out of ten are discovered. And now let me take a good look at that box and its contents."

He lifted the box from the safe to the table, and narrowly scrutinised its exterior, especially about the hasp, where the padlock had been. "Either the thief was an experienced hand," he said, "or he took some steady practice with a few such padlocks as this before setting to work. There are no signs of banging about or slipping of tools anywhere."

"But, of course, banging or anything violent would have been noticed in a place like this," Mr. Bell remarked.

"In office hours, yes," responded Hewitt. "But we mustn't forget that office hours are only seven or eight out of the twenty-four."

"But you don't suspect burglary, do you?"

"I'm afraid, as yet, I've precious little ground for suspecting anything definite," Hewitt answered; "but we must keep awake to every possibility. Now let us see the dummies." He turned them over, and loosened them wherever they were tied. "Yes," he remarked, "quite neatly done. Filled in with ordinary blank foolscap, such as, no doubt, you have in your office-but, then, it is in every other office, too; every stationer has it by the ream. No marks anywhere-no old newspapers, nothing that could give the shadow of a clue." He dropped the last of the papers, and turned to his client. "Mr. Bell," he said, "this thing has been thought out to the last inch. There is something like genius in this robbery-if genius is the capacity for taking pains. My advice to you is to call in the Scotland Yard people at once."

"Do you mean you can do nothing?" asked Mr. Bell despairingly. "Don't tell me that, Mr. Hewitt!"

"No, I don't mean that," Hewitt answered. "I mean that until I have had time to think the thing over very thoroughly I can't tell what I can or ought to do. Meantime, I think the police should know; not because I think they can see farther into the thing than I can-for, indeed, I don't think they can; but simply because the thief is getting a longer start every moment, and the police are armed with powers that are not at my disposal. They can get search warrants, stop people at ports and railway stations, arrest suspects-do a score of things that will be necessary. Send to Scotland Yard and get Detective Inspector Plummer, if he's available-he's as good a man as they have. Tell him that you've engaged me, or, better still, write a note to the Scotland Yard authorities, and let me have it, to send or not as I think best, after I have turned the thing over in my mind. I shall take one good look round this office, and then run back to my rooms for an hour or two's hard consideration of whatever I may see. One or two small things I have seen already-though I'd rather not mention them till I've made up my mind how they bear. Matters seem likely to have gone so far that perhaps the regular police course of catching the thief first will be the best plan, if it can be done. Meantime, it will be my business to keep my eye first on the recovery of the bonds. But I think we must have the police, Mr. Bell. Now, I'll take my general look round."

III

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 sc.r.a.p," 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 n.o.ble, 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 gla.s.s door from which a bill had recently been torn.

"Why, it's let!" said Mr. Bell.

"Yes, sir," a.s.sented 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 trespa.s.s 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 s.n.a.t.c.hed 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 grat.i.tude, 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 gla.s.ses; "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 advantage of his position in that little inner room to get at the safe some day when it was open and when you were engaged in your own private inner room with a client, so leaving the safe unwatched. He was provided with a spare patent padlock and key, of the sort you used on that black box, and his confederate had drilled him in the trick of breaking that particular sort of padlock open, with other spare specimens. He got his opportunity this morning."

"Only this morning?"

"This morning, I think, else we should never have got these bonds back, nor even have heard of them again. I think you said you were engaged with a client for half an hour?"

"Yes, from about half-past ten to eleven."

"That was his chance, and he took it. He broke the padlock, took out the bonds, subst.i.tuted the dummies he had already prepared in his own desk, and locked the box again with the new padlock. Meantime Hunt had paid a deposit, pending references, on the office below-the nearest empty room. Of course, he wouldn't get the key until the tenancy was finally accepted-which he never intended it should be. But he easily arranged to have the door left unlocked for a day or two, on some convenient excuse-arranging decorations, or what not. And the bill was taken down, so that prospective and prospecting tenants were kept away. The bonds being stolen, Henning took the first opportunity of carrying them to the empty office-probably piecemeal-a thing he could easily manage almost under your nose, before you were aware of your loss. There he was to conceal them, either in the chimney, under the boards, or in the ventilator, as he might find convenient-and he found the ventilator most convenient. Then he was to apprise his confederate of the fact that the robbery had been effected in order that Hunt might come and quietly fetch the plunder away. The message was to take an ingenious form. Hunt was to have a fellow waiting about in the street, and as soon as Henning could get out-say to lunch-he was just to send the key by this messenger-the key with which he had locked the new padlock on the black box. You see the advantages of that simple arrangement. First, the key, which is evidence, is got rid of in a safe and effectual way-a thing that couldn't be done as well by merely flinging it away on or near the premises, where it might be found. Next, the message is perfectly secret-the messenger could never guess what the key meant, nor could any other person not in the confederate's confidence. And, at the same time, the key tells all that is necessary; the robbery has been effected-come and remove the plunder.

"But something unforeseen happens. No sooner are the bonds stolen and safely hidden than you go to the box, find something wrong with the lock, break it open and discover the loss. This was a thing that they trusted would not happen till after the bonds were safely got away. More, I am sent for, the clerks are kept in from lunch, and so on. Henning gets into a funk, and resolves to send a message of special urgency to his confederate. For that purpose he uses a cypher which the two have agreed upon-the most ingenious cypher I have ever seen used for the purpose. He doesn't wish to make his message any more conspicuous than he need, so he writes his cypher on this sc.r.a.p of paper and rolls it inside the key-probably another expedient agreed upon in case of necessity. Then the key goes into an envelope, for greater security of the cypher message, and the messenger gets it when Henning is at last released for lunch. What happened to the message we know; and here it is.