In the story books your detective scans with eagle eye the surface of the floor for microscopic evidences of crime.  His mind leaps from a cigar ash to a piece of banana peel and thence to what the family had for dinner.  His brain is working all the time.  It is, of course, all quite wonderful and most excellent reading, and the old-style sleuth really thought he could do it!  Nowadays, while the fake detective is snooping around the back piazza with a telescope, the real one is getting the “dope” from the village blacksmith or barber or the waitress at the station.  He may not be highly intelligent, but he knows the country, and, what is more important, he knows the people.  All the brains in the world cannot make up for the lack of an elementary knowledge of the place and the characters themselves.  It stands to reason that no strange detective could form as good an opinion as to which of the members of your household would be most likely to steal a piece of jewelry as you could yourself.  Yet the old-fashioned Sherlock knew and knows it all.

One of the best illustrations of the practical necessity of some first-hand knowledge is that afforded by the recovery of a diamond necklace belonging to the wife of a gentleman in a Connecticut town.  The facts that are given here are absolutely accurate.  The gentleman in question was a retired business man of some means who lived not far from the town and who made frequent visits to New York City.  He had made his wife a present of a fifteen thousand-dollar diamond necklace, which she kept in a box in a locked trunk in her bedroom.  While she had owned the necklace for over a year she had never worn it.  One evening having guests for dinner on the occasion of her wedding anniversary she decided to put it on and wear it for the first time.  That night she replaced it in its box and enclosed this in another box, which she locked and placed in her bureau drawer.  This she also locked.  The following night she decided to replace the necklace in the trunk.  She accordingly unlocked the bureau drawer, and also the larger box, which apparently was in exactly the same condition as when she had put it away.  But the inner box was empty and the necklace had absolutely disappeared.  Now, no one had seen the necklace for a year, and then only her husband, their servants, and two or three old friends.  No outsider could have known of its existence.  There was no evidence of the house or bureau having been disturbed.

A New York detective agency was at once retained, which sent one of its best men to the scene of the crime.  He examined the servants, heard the story, and reported that it must have been an inside job—­that there was no possibility of anything else.  But there was nothing to implicate any one of the servants, and there seemed no hope of getting the necklace back.  Two or three days later the husband turned up at the agency’s office in New York, and after beating about the bush for a while, remarked: