For example, if you are receiving anonymous letters, the writer of which accuses you of all sorts of unpleasant things, you would, of course, much prefer to find out who it is and stop him quietly than to turn over the correspondence to the police and let the writer's attorneys publicly cross-examine you at his trial as to your past career. Even if a diamond necklace is stolen from a family living on Fifth Avenue, there is more than an even chance that the owner will prefer to conceal her loss rather than to have her picture in the morning paper. Yet she will wish to find the necklace if she can. When the matter has no criminal side at all, the police cannot be availed of, although we sometimes read that the officers of the local precinct have spent many hours in trying to locate Mrs. So-and-So's lost Pomeranian, or in performing other functions of an essentially private nature--most generously. But if, for example, your daughter is made the recipient, almost daily, of anonymous gifts of jewelry which arrive by mail, express, or messenger, and you are anxious to discover the identity of her admirer and return them, you will probably wish to engage outside assistance. Where will you seek it? You can do one of two things: go to a big agency and secure the services of the right man, or engage such a man outside who may or may not be a professional detective. I have frequently utilized with success in peculiar and difficult cases the services of men whom I knew to be common-sense persons, with a natural taste for ferreting out mysteries, but who were not detectives at all. Your head bookkeeper may have real talents in this direction--if he is not above using them. Naturally, the first essential is brains--and if you can give the time to the matter, your own head will probably be the best one for your purposes. If, then, you are willing to undertake the job yourself, all you need is some person or persons to carry out your instructions, and such are by no means difficult to find. I have had many a case run down by my own office force--clerks, lawyers, and stenographers, all taking a turn at it. Why not? Is the professional sleuth working on a fixed salary for a regular agency and doing a dozen different jobs each month as likely to bring to bear upon your own private problem as much intelligence as you yourself? There is no mystery about such work, except what the detective himself sees fit to enshroud it with. Most of us do detective work all the time without being conscious of it. Simply because the matter concerns the theft of a pearl, or the betraying of a business or professional secret, or the disappearance of a friend, the opinion of a stranger becomes no more valuable. And the chances are equal that the stranger will make a bungle of it.