"Oh! Simply this. Some time ago one of our listeners caught an earlier message near Socorro, which gave us a hint as to where the messages were crossing the border. We at once sent a number of expert army wireless men into that part of the border region to listen in. One message was picked up at a point fifty miles north of the boundary, but it was very faint. Along the line itself the radio men have never detected a sound. Yet your boys are intercepting the messages here, so we know that they are being sent regularly. That made us think that perhaps the messages were being telephoned the last lap of the journey and carried over the line by a person."
"I have no doubt that your theory is correct," said Captain Hardy.
"Well, last night we thought for a time that we had the man who was carrying the messages. When my operator here picked up the message yesterday afternoon, I instantly sent a message to my subordinate in charge of the work in the El Paso district, telling him of the sending of the message and urging extra vigilance. Yet not one of the radio men heard a sound. But in the middle of the night my men grabbed a Mexican who had slipped past the armed guards and was starting to wade across the Rio Grande to Mexico."
"Excellent!" cried Captain Hardy.
"Good enough as far as it went," said the Chief, with a wry face, "but it didn't go far enough. The fellow was only a smuggler."
"Are you certain, Chief?"
"Sure as preaching, worse luck."
"Was the man searched thoroughly?"
"Now, Captain, what do you think the secret service is, anyway? Was he searched! It would make your eyes pop out if you'd see the way we go through a man. We strip him and give him a lemon bath to bring out any secret message that might be written on his skin, and we take his clothes apart scientifically, I tell you. No, this fellow had nothing incriminating on him. After a grueling examination, he admitted that he had crossed the line to smuggle in some tobacco. However, it's only a question of time until we do put our finger on the missing link. Then for a great raid!"
"How I shall welcome that day," said Captain Hardy. "This spy business is never absent from my thoughts, with its menace to our boys on the ocean."