"There must be another X. Y. Z.," said he, approaching the window of the post-office and handing back all the letters he had received, with the exception of the one in the blue envelope, which with a quick movement he had separated from the rest and thrust into his coat-pocket. "I can lay claim to none of these." And with a repetition of his easy bow he turned away and hurriedly quitted the store, followed by the eyes of clerks and customers, to whom he was evidently as much of a stranger as he was to me. Without hesitation I went to the door and looked after him. He was just crossing the street to the tavern on the other side of the way. I saw him enter, felt that he was safe to remain there for a few minutes, and conscious of the great opportunity awaiting me, hastened back to the postmaster. "Well," cried I, in secret exultation, "our plan has worked admirably. Let me see the letters. As they have been opened, and through no fault of ours, a peep at them now in the cause of justice will harm none but the guilty." The postmaster demurred, but I soon overcame his scruples; and taking down the letters once more, hastily investigated their contents. I own that I was considerably disappointed at the result. In fact, I found nothing that pointed toward the counterfeiters; only in each letter a written address, together with fifty cents' worth of stamps. "Some common fraud," I exclaimed. "One of those cheap affairs where, for fifty cents enclosed, a piece of information calculated to insure fortune to the recipient is promised by return of mail." And disgusted with the whole affair I bundled up the letters, and was about to replace them in the box for the third time when I discovered that it still held a folded paper. Drawing this out, I opened it and started in fresh amazement. If I was not very much mistaken in the appearance of the letter in the blue envelope which I had seen the young man read with so much interest, this was certainly it. But how came it here? Had I not seen him thrust it back into its envelope and afterward put envelope and all into his pocket? But here was no envelope, and here was the letter. By what freak of necromancy had it been transferred from its legitimate quarters to this spot? I could not imagine. Suddenly I remembered that his hand had been full of the other letters when he put, or endeavored to put, this special one back into its envelope, and however unaccountable it may seem, it must be that from haste or agitation he had only succeeded in thrusting it between two letters instead of into the envelope, as he supposed. Whether or not this explanation be true, there was no doubt about my luck being in the ascendant. Mastering my satisfaction, I read these lines written in what appeared to be a disguised hand.