It is estimated that more than a hundred thousand spies and agents have been in the service of the various countries during the War. Several thousand have been captured and several hundred have been executed. The German spy system in the United States alone was a powerful organization at the beginning of the war. But the American Secret Service, one of the greatest organizations of its kind in existence, thwarted their plots, interned them in large numbers, and drove such men as Boy-Ed and von Papen from our shores. The interception of the Zimmerman note to Mexico, the revelations of the Swedish duplicity in Argentine, the discovery of Bolo, the French financier, the plots in India--and hundreds of others have been exposed by the genius of the United Secret Service. Most of these stories cannot be told until long after the War, but a few of them, gathered from American and European sources, are told here. I--HOW THE SPIES WORK IN EUROPE The extraordinary ingenuity shown by spies in securing the plans of other countries' fortifications has been amply illustrated in the war, although, of course, we know but a little part of what the spies have accomplished. A woman was caught at the French frontier seeking to enter Switzerland and presumably intending to return to Germany or Austria. She was thoroughly searched by a matron, as is customary in such cases, but nothing was found. Certain actions of hers, however, had given rise to serious suspicions, and one of the cleverest officers of the French Secret Service was detailed to examine her. He applied several tests to her. He finally obtained what he wanted by seating her, in an undraped condition, tied to a chair, before a warm fire. "Brutes, you are going to burn me alive!" she shrieked as she was forced into a chair. "Be calm, madame," said the officer. "We only want to admire your beautiful back." There appeared on the ample back of this fair-haired lady an elaborate design. To the experienced eye of the officer it represented a plan of one of the most important French fortresses. The number of guns, their sizes and positions were shown. The angles, sallies and extent of the fortifications were clearly indicated. The weak spots in the defense were made clear. This fortress had been entirely made over since the outbreak of the war, and it was of vital importance to the Germans to know its present arrangements. A German spy in France, evidently a man with military knowledge, had obtained access to the fortress, but there was but slight chance of his getting home with his knowledge. He had, therefore, used the young woman as an innocent looking agent.