"That might have come from a search-light, swiftly operated," thought Lieutenant Hal, with a start. After a moment's reflection, he hurried on board the boat. "Mate," he directed, "shove off and steam out just past the end of the pier." "Why----" began the mate wonderingly. "Obey the order, sir!" As the boat moved slowly into open water Hal, standing by the search-light, gave another order: "Switch on this light, mate." "But your captain said----" "Switch on the light, man! Be quick about it!" As the light gleamed out Lieutenant Hal turned its broad flare up the river. Just on the edge of the beam he picked up a motor boat of considerable size. The other craft was some three miles up the river, headed due south across to the Mexican border. In the instant that the man in charge of the motor boat discovered the search-light, he crowded on more speed. "My plain orders are to remain here," quivered Lieutenant Hal to himself. "If I obey, even during a five minutes' delay, that craft will outfoot us to Mexico, and a cargo of arms will be on the other shore. There's no time to communicate with Captain Foster. What on earth shall I do--disobey and face the chance of trial for disobedience of orders?" CHAPTER XVI AFTER SWIFT GAME It was a ticklish position, and one that called for quick decision. If Lieutenant Overton ordered the tug back to the pier and remained where he was, he would be but obeying explicit orders. No blame could afterward attach to him, no matter how many boats got across. At the same time the young Army officer knew that he was stationed here for the express purpose of preventing any arms being smuggled over to Mexico. "Even though I capture a boat with ten thousand stands of arms aboard," flashed swiftly through the Army boy's mind, "Captain Foster can still say that I disobeyed orders. Yet if I obey orders there's no telling what mischief may be done." "Yet it seems to me that, when I am set to watch a violation of the national law, my first duty is to try to catch any one who attempts to violate the law," quivered the lieutenant. Suddenly Hal turned to the mate. "Go ahead, man--full speed! Catch that boat yonder!" No reply did the mate make, but he rang one bell for half-speed ahead. This he presently followed with the signal for full speed. The tug's propeller churned the water astern. For a craft of this kind the tug was now moving fast. Hal steadily held the ray of the search-light on the stranger. "Can't you hump a little more speed out of this tub?" the young officer demanded. "I can't signal for any more," replied the mate, his hands on the spokes of the wheel. "Why don't you ask the engineer?" Young Overton quickly summoned a soldier and sent him to the engineer with a message calling for more speed. After another minute the increase in speed was easily discernible. "But that boat's getting away from us," cried Lieutenant Overton, with irritation in his voice.