So the cruise continued. Halstead was soon on deck again, but the young skipper found Darrin so enjoying his trick at the wheel that Skipper Tom merely stood near to take the trick again whenever the young ensign showed signs of being tired of his job. It was late in the night, and the "Restless" was making her third trip up the river before anything happened. For some time the young Army and Navy officers had felt more or less bored with the monotony of these hours of tiresome waiting. Tom Halstead had stretched himself out on the deck-house for rest, though not to nap, and Hank Butts was at the wheel, while Joe dozed lightly on a seat in the engine-room. All of the enlisted men had crowded below, and were dozing. "Look sharp, there!" cried Lieutenant Hal, suddenly, as he sprang to Hank's side. "There's a craft moving out from the American shore, about a mile upstream, isn't there!" "Something moving, for sure," replied Hank, peering through the darkness. "A motor boat?" "It must be." "Trail her. Get in closer." Skipper Tom Halstead now came forward, though he did not take the wheel from Hank. "The search-light is ready, whenever you want it, Lieutenant," remarked the youthful motor boat skipper. "The use of the light might save the fellows on the other craft some guessing," smiled Lieutenant Hal. "I want to keep 'em guessing as long as possible." "I'll kick on more speed," proposed Hank, reaching for the deck controls. "Wait until you get orders," interposed Skipper Tom Halstead. "This is government business, Hank, and we're not government officers, so we'll act only under orders." It was evident that those aboard the craft upstream had made out the pursuing motor boat. The unknown craft was now heading straight across the stream, and kicking on some speed. "How fast is the stranger going?" asked Lieutenant Overton. "Twenty miles an hour, as nearly as I can guess," replied Skipper Tom. "How fast can you go?" "Twenty-six to twenty-eight miles." "Crowd it about all on, then. I don't want to have that other craft get too close to Mexico before we push up alongside." "All speed, Joe, and do it quick!" Skipper Tom called down into the engine-room. Almost at once the "Restless" earned her name by fairly leaping forward through the water. Then the chase began in earnest. "Noll, pass the word below for a sergeant and six privates," directed Lieutenant Hal, in a low tone. The enlisted men came up, taking their places on deck. "Does the lieutenant want us to load our pieces?" called the sergeant quietly. "Not yet," was Hal's reply, passed back by Noll. Then, on board the pursuing craft, all settled down to absolute quietness, save for the running of the machinery. The distance between the two boats was rapidly closing up, for it was plain that the other boat had started at full speed as soon as she sighted the pursuer.