Beside the bookcase in the room which Bill Quinn likes to dignify by the name of "library"--though it's only a den, ornamented with relics of scores of cases in which members of the different government detective services have figured--hangs a frame containing four letters, each in a different handwriting. Beyond the fact that these letters obviously refer to some secret in the lives of the persons to whom they are addressed, there is little about them that is out of the ordinary. A close observer, however, would note that in none of the four is the secret openly stated. It is only hinted at, suggested, but by that very fact it becomes more mysterious and alarming. It was upon this that I commented one evening as I sat, discussing things in general, with Quinn. "Yes," he agreed, "the writer of those letters was certainly a genius. As an author or as an advertising writer or in almost any other profession where a mastery of words and the ability to leave much to the imagination is a distinct asset, they would have made a big success." "They?" I inquired. "Did more than one person write the letters?" "Don't look like the writing of the same person, do they?" countered Quinn. "Besides, that was one of the many phases of the matter which puzzled Elmer Allison, and raised the case above the dead level of ordinary blackmailing schemes." * * * * * Allison [Quinn went on, settling comfortably back in his big armchair] was, as you probably remember, one of the star men of the Postal Inspection Service, the chap who solved the mystery of the lost one hundred thousand dollars in Columbus. In fact, he had barely cleared up the tangle connected with the letters when assigned to look into the affair of the missing money, with what results you already know. The poison-pen puzzle, as it came to be known in the department, first bobbed up some six months before Allison tackled it. At least, that was when it came to the attention of the Postal Inspection Service. It's more than likely that the letters had been arriving for some time previous to that, because one of the beauties of any blackmailing scheme--such as this one appeared to be--is that 90 per cent of the victims fear to bring the matter to the attention of the law. They much prefer to suffer in silence, kicking in with the amounts demanded, than to risk the exposure of their family skeletons by appealing to the proper authorities. A man by the name of Tyson, who lived in Madison, Wisconsin, was the first to complain. He informed the postmaster in his city that his wife had received two letters, apparently in a feminine handwriting, which he considered to be very thinly veiled attempts at blackmailing. Neither of the letters was long. Just a sentence or two. But their ingenuity lay in what they suggested rather than in their actual threats. The first one read: