“Well, I think we must wait for a little more material. After all, you have nothing to complain of. You have received your rent, and he is not a troublesome lodger, though he is certainly an unusual one. He pays you well, and if he chooses to lie concealed it is no direct business of yours. We have no excuse for an intrusion upon his privacy until we have some reason to think that there is a guilty reason for it. I’ve taken up the matter, and I won’t lose sight of it. Report to me if anything fresh occurs, and rely upon my assistance if it should be needed.

“There are certainly some points of interest in this case, Watson,” he remarked when the landlady had left us. “It may, of course, be trivial - individual eccentricity; or it may be very much deeper than appears on the surface. The first thing that strikes one is the obvious possibility that the person now in the rooms may be entirely different from the one who engaged them.”

“Why should you think so?”

“Well, apart from this cigarette-end, was it not suggestive that the only time the lodger went out was immediately after his taking the rooms? He came back - or someone came back - when all witnesses were out of the way. We have no proof that the person who came back was the person who went out. Then, again, the man who took the rooms spoke English well. This other, however, prints ‘match’ when it should have been ‘matches.’ I can imagine that the word was taken out of a dictionary, which would give the noun but not the plural. The laconic style may be to conceal the absence of knowledge of English. Yes, Watson, there are good reasons to suspect that there has been a substitution of lodgers.”

“But for what possible end?”

“Ah! there lies our problem. There is one rather obvious line of investigation.” He took down the great book in which, day by day, he filed the agony columns of the various London journals. “Dear me!” said he, turning over the pages, “what a chorus of groans, cries, and bleatings! What a rag-bag of singular happenings! But surely the most valuable hunting-ground that ever was given to a student of the unusual! This person is alone and cannot be approached by letter without a breach of that absolute secrecy which is desired. How is any news or any message to reach him from without? Obviously by advertisement through a newspaper. There seems no other way, and fortunately we need concern ourselves with the one paper only. Here are the Daily Gazette extracts of the last fortnight. ‘Lady with a black boa at Prince’s Skating Club’ - that we may pass. ‘Surely Jimmy will not break his mother’s heart’ - that appears to be irrelevant. ‘If the lady who fainted in the Brixton bus’ - she does not interest me. ‘Every day my heart longs- -’ Bleat, Watson - unmitigated bleat! Ah, this is a little more possible. Listen to this: ‘Be patient. Will find some sure means of communication. Meanwhile, this column. G.’ That is two days after Mrs. Warren’s lodger arrived. It sounds plausible, does it not? The mysterious one could understand English, even if he could not print it. Let us see if we can pick up the trace again. Yes, here we are - three days later. ‘Am making successful arrangements. Patience and prudence. The clouds will pass. G.’ Nothing for a week after that. Then comes something much more definite: ‘The path is clearing. If I find chance signal message remember code agreed - one A, two B, and so on. You will hear soon. G.’ That was in yesterday’s paper, and there is nothing in to-day’s. It’s all very appropriate to Mrs. Warren’s lodger. If we wait a little, Watson, I don’t doubt that the affair will grow more intelligible.”

So it proved; for in the morning I found my friend standing on the hearthrug with his back to the fire and a smile of complete satisfaction upon his face.