'Having written two or three letters of this kind without success, her persecutor might then send an envelope like this to show her that he was thoroughly resolved to carry out his threats unless she agreed to his terms. But as a first move it can mean nothing; and the person to whom it is addressed, knowing that it has already been seen by the postman, the servants, and perhaps by others, would in any case be driven to hand it over to her friends. Miss Hawtrey has received no preliminary letters, therefore it is clear to me that this is not an attempt to extort money. We have nothing, therefore, to fall back upon but the idea of sheer malice, and I have known so many cases of wanton and ingenious mischief-making, arising from such paltry and insufficient causes, that I can be surprised at nothing.' 'Still, I don't see how anyone could do such an infamous and cruel thing as this, Danvers, without some real cause for malice. My daughter is altogether unconscious of having an enemy, there is nothing for us to go upon, and I do not see how the business of discovery is to be commenced.' 'At present, certainly, we seem to have no clue to help us. The letter was posted, you see, in London, but that is of no use whatever; were it from a small country town or rural district the matter would be comparatively easy, but London is hopeless. I have no doubt some more letters of this kind will come, and I should say that although the post-marks may afford you no information, the postal authorities might be able to help you. I do not know whether the stamps at all the district post offices are identical, but it is possible that there may be some private mark on them, some little peculiarity, by which the post-office people would be able to tell you the office at which it was posted. 'But even this would help us but little, as the letters are collected and sent to the central district office, and are there, I believe, stamped. At any rate, I see no use in your employing a man now, Mr. Hawtrey. If you get a clue, even the smallest, I have a fellow in my mind's eye who would, I think, suit you. He was at one time a clerk with Buller and Sons. They gave up the criminal part of their business when the eldest son, who had charge of that branch, died, and this man, Slippen, was no longer wanted. He then set up on his own account, as a sort of private detective. He has been employed in two or three delicate cases in which I have held briefs, and is certainly a very shrewd fellow.' 'It would be a relief to me to be doing something,' Mr. Hawtrey said. 'I think I should like to see the man.' Danvers was silent for a minute.