Waiting with the eagerness of the greyhound in leash, David Steel was more annoyed and vexed over the disappearance of the wounded Van Sneck than he cared to admit. He had an uneasy feeling that the unseen foe had checkmated him again. And he had built up so many hopes upon this strangely-uninvited guest of his. If that man spoke he could tell the truth. And both Cross and Bell had declared that he would not die.

David found Cross in a frame of mind something like his own. It was late in the afternoon before it transpired that Van Sneck was gone, and, unfortunately, David did not know where to find Bell just at the moment. Cross had very little to say.

"A most unpleasant incident," he remarked. "But these things will happen, you know. We have been so busy lately, and our vigilance has been slightly relaxed. Oh, it is impossible to guard against everything, but he is certain to be found."

"You don't think," David suggested, "that anybody secretly connected with the man's past—"

"No, I don't," Cross snapped; "that would be impossible. The man had something on his mind, and so far as bodily condition was concerned he was getting quite strong again. In his dazed state he got up and dressed himself and went away. He seems to have been seeking for somebody or something for days. We are certain to have him again before long."

With which poor consolation David returned home again. He was restless and desirous of human companionship. He even resented it, as a kind of affront, that his mother had chosen at this time to go to Hassocks to stay with an old friend for a couple of days. That Mrs. Steel knew practically nothing of her son's trouble counted for naught. Therefore it was with something akin to pleasure that David found Ruth Gates waiting in the drawing-room for him when he came in from his walk on the following afternoon. Nothing had been heard of Van Sneck in the meantime, but thanks to Chris's telephone message late the previous night he had got in touch with Bell, who was coming south without delay.

There was a look of shy pleasure in Ruth's eyes and a deep carmine flush on her cheeks.

"You don't think that this is very bold of me?" she asked.

"I am pretty Bohemian in any case," David laughed, as he looked down fondly into the shy, sweet eyes. "And I'm too overjoyed to see you to think about anything else. I wish my mother was at home. No, I don't, because I have you all to myself."

"David! On an occasion like this you ought to be the pink of propriety.
Do you know, I believe that I have made a great discovery?"

"Indeed, little girl! And what have you found out?"

"Well, you must tell me something before my discovery seems valuable. David, you are a close student of human nature. Is it possible for men of phenomenal cunning to make careless mistakes? Do the most clever criminals ever make childish blunders?"

"My dear child, if they didn't the police would have very little chance. For instance, I have discovered how those enemies of ours got hold of the notepaper that lured Van Sneck here. They sent a messenger to Carter's, in East Street, presumedly knowing that my dies were there, and ordered a quarter of a ream of paper and envelopes. These were to be sent to an address in East Grinstead in a hurry. Now, that was very clever and smart, but here comes the folly. Those people, in the stress of business, actually forgot to ascertain the cost and pay for the paper, so that it was down yesterday in my last quarter's bill. Oh, yes, I assure you, the most brilliant criminals do the most incredibly foolish things."

Ruth looked relieved. Her pretty features relaxed into a smile.

"Then I fancy Reginald Henson has done so," she said. "I fancy I have solved the mystery of the cigar-case—I mean, the mystery of the one I bought."

"And which was changed for the one purchased at Walen's, hence these tears. But Lockharts say that our case was really purchased by an American."

"Yes, I know. And I fancy that the manager honestly thought so. But I think I can explain that."

It was David's turn to look up eagerly.

"Do you mean it?" he exclaimed. "It will make a wonderful difference if you can. That has been one of the most bewildering knots of the whole puzzle. If we could only trace the numbers of those notes, I suppose changed at the same time as the cigar-case."

"Indeed they were not," Ruth cried. "I have ascertained that the case was changed by Henson, as you and I have already decided. Henson made the exchange not at the time we thought."

"Not when you left the package on the table for him to see?"

"No; at least I can't say. He had the other case then, probably, passed on to him by Van Sneck. Or perhaps he merely ascertained what I had purchased. That was sufficient for his purpose. Of course he must have found out all about our scheme. After I had laid my cigar-case on your doorstep a man quietly changed it for the other purchased at Walen's. But this is the alternate theory only. Any way, I am absolutely certain that you got exactly the same notes that we had placed in the original case."

"That might be," David said, thoughtfully. "But that does not explain the fact that Lockhart's sold your case to an American at the Metropole."

"I fancy I can even explain that, dear. My uncle came down suddenly to-day from London. He wanted certain papers in a great hurry. Now, those papers were locked up in a drawer at 219 given over specially to Mr. Henson. My uncle promptly broke open the drawer and took out the papers. Besides those documents the drawer contained a package in one of Lockhart's big linen-lined envelopes—a registered letter envelope, in fact. My uncle had little time to spare, as he was bound to be back in London to-night. He suggested that as the back of the drawer was broken and the envelope presumably contained valuables, I had better take care of it. Well, I must admit at once that I steamed the envelope open. I shouldn't have done so if Lockhart's name had not been on the flap. In a little case inside I found a diamond bracelet, which I have in my pocket, together with a receipted bill for seventy odd pounds made out to me."

"To you?" David cried. "Do you mean to say that—"

"Indeed I do. The receipt was made out to me, and with it was a little polite note to the effect that Messrs. Lockhart had made the exchange of the cigar-case for the diamond bracelet, and that they hoped Miss Gates would find the matter perfectly satisfactory."

David was too astonished to say anything for the moment. The skein was too tangled to be thought out all at once. Presently he began to see his way.

"Under ordinary circumstances the change seems impossible," he said. "Especially seeing that the juggling could not have been done without both the cases—but I had forgotten how easily the cases were changed. I have it! What is the date of that letter?"

Ruth slowly unfolded a document she had taken from her purse.

"The day following what you call your great adventure," she said. "Henson or somebody took the real case—my case—back to Lockhart's and changed it in my name. I had previously been admiring this selfsame bracelet, and they had tried to sell it to me. My dear boy, don't you see this is all part of the plot to plunge you deeper and deeper into trouble, to force us all to speak to save you? There are at least fifteen assistants at Lockhart's. Of course the ultimate sale of the cigar-case to this American could be proved, seeing that the case had got back into stock again, and at the same time the incident of the change quite forgotten. And when you go and ask questions at Lockhart's—as you were pretty sure to do, as Henson knew—you are told of the sale only to the American. Depend upon it, that American was Henson himself or somebody in his pay. David, that man is too cunning, too complex. And some of these days it is going to prove his fall."

David nodded thoughtfully. And yet, without something very clever and intricate in the way of a scheme, Henson could not have placed him in his present fix.

"There is only one thing to be done," he said. "You and I must go down to Lockhart's and make a few inquiries. With that diamond bracelet and letter in your possession you should have no difficulty in refreshing their memories. Will you have some tea?"

"I am too excited," Ruth laughed. "I couldn't eat or drink anything just at present. David, what a lovely house you have."

"I'm glad to hear that you are going to like it," David said, drily.

Lockhart's received their customers in the usual courtly style. They were sorry they had no recollection of the transaction to which madam referred. The sale of the bracelet was clear, because that was duly and properly recorded on the books, and as indeed was the sale of the gun-metal cigar-case to an American gentleman at the Metropole. If madam said that she had purchased the cigar-case, why—still the polite assistant was most courteously incredulous.

The production of the letter made a difference. There was a passing of confidences from one plate-glass counter to another, and presently another assistant came forward. He profoundly regretted that there had been a mistake, but he remembered the incident perfectly. It was the day before he had departed on his usual monthly visit to the firm's Paris branch. Madam had certainly purchased the cigar-case; but before the sale could be posted in the stock ledger madam had sent a gentleman to change the case for the diamond bracelet previously admired. The speaker had attended to both the sale and the exchange; in fact, his cab was waiting for him during the latter incident.

"I trust there is nothing wrong?" he asked, anxiously.

"Not in the least," Ruth hastened to reply. "The whole matter is a kind of comedy that I wanted to solve. It is a family joke, you understand. And who made the exchange?"

"Mr. Gates, madam. A tall gentleman, dressed in—"

"That is quite sufficient, thank you," said Ruth. "I am sorry to trouble you over so silly a matter."

The assistant assured madam with an air of painful reproach that nothing was counted a trouble in that establishment. He bowed his visitors out and informed them that it was a lovely afternoon, a self-evident axiom that the most disputatious could not well deny.

"You see how your inquiries might have been utterly baffled but for this find of mine," Ruth said, as the two went along North Street. "We shall find presently that the Metropole American and Reginald Henson are one and the same person."

"And you fancy that he made the exchange at Lockhart's?"

"I feel pretty certain of it," Ruth replied. "And you will be sure later on to find that he had a hand in the purchase of the other cigar-case from Walen's. Go to Marley's and get him to make inquiries as to whether or not Walen's got their case down on approval."

David proceeded to do so without further delay. Inspector Marley was out, but David left a message for him. Would he communicate by telephone later on? Steel had just finished his dinner when Marley rang him up.

"Are you there? Yes, I have seen Walen. Your suggestion was quite right. Customer had seen cigar-case exactly like it in Lockhart's, only too dear. Walen dealt with some manufacturers and got case down. Oh, no, never saw customer again. That sort of thing happens to shopkeepers every day. Yes. Walen thinks he would recognise his man again. Nothing more? Good-night, sir."