"Oh, you're going to have plenty of room here," decided Captain Foster, after a brief look over the trim little motor craft.

"I'm glad of that," sighed Dave Darrin, "for, as an interloper, I'd have to go ash.o.r.e the first one if the quarters were crowded."

"Mr. Overton, direct Sergeant Havens and his men to come aboard. Mr.

Prescott, you'll look out for your squad, of course."

"Certainly, sir."

"Mr. Overton, as soon as you have your men aboard, give the skipper his word to start. You will cruise without lights, unless need for them arises. While cruising, do not go above nine miles an hour. Reserve greater speed for pursuit. First, you will cruise eight miles up the river, then eight miles below this point, and so on through the night until a half-hour before daylight. As much as you can, avoid showing your craft to any prowlers by the sh.o.r.es. Keep things dark aboard the boat, and voices low."

By this time the enlisted men had come aboard, many of them going below to the cabin.

"You may start, now," continued Captain Poster, jumping to the pier.

"Catch anything you can that has arms aboard for the other frontier.

Good-bye and good luck!"

Hardly had the motor boat gotten under way when the tug, with Corporal Shimple and four men aboard, also left her berth. The tug went only a short distance out into the stream, then cast anchor for the night. The tug was to be held in reserve, and at the same time her mate and crew were thus prevented from communicating any news about the motor boat to possible Mexican lurkers on sh.o.r.e.

The five young officers of the two services had seated themselves on top of the deck-house at the rear of the bridge-deck. Hank b.u.t.ts sat midway down on the deck-house, yawning as though he would like to turn in.

After he had got his engine working smoothly Engineer Joe Dawson came up from the engine room forward, taking his stand beside Skipper Tom Halstead.

For five minutes Joe was silent, as the boat kept on up the Rio Grande.

He half-turned, once in a while, to cast a covertly-admiring glance at the young officers seated at their rear. At last Joe whispered exultantly in his chum's ear:

"Tom, that's a real fighting bunch."

"You've hit the truth at first trial," returned Skipper Tom, in an undertone, as he kept his glance ahead over the river.

"I'm not much given to exaggeration, am I, Tom?"

"I never knew that you had an acquaintance with exaggeration," Halstead answered.

"Then perhaps you'll believe me, Tom, when I tell you that I'd follow those officers over Niagara or into Vesuvius, if they happened to be bound either way."

"I know you would, Joe," Tom answered, without smiling, for he knew his chum through and through.

"Tom, those young officers would _a.s.say up a big lot of fight to the ton_!"

Having thus relieved himself of that strong conviction Joe Dawson seated himself on the roof of the forward house and did not speak again for twenty minutes.

By the time that the eight miles upstream had been covered, and Skipper Tom Halstead had headed the boat down again for its straight sixteen-mile run, he called down to his chum:

"Joe, will you come up and hold the wheel for me for two or three minutes?"

"Coming," Dawson sang cheerily.

But Dave Darrin stepped forward with:

"Skipper, can't _I_ hold the wheel for you?"

"Have you ever handled a boat before, sir?" Tom queried, giving this young man, who was in civilian dress, a keen though good-humored look.

"At least twice," Darrin modestly a.s.sured him.

"How big a boat?"

"Up to sixteen thousand tons," Darrin replied, without cracking a smile.

"A wise man is always cautious, Halstead," sang out Lieutenant Prescott gleefully, "but the man you're talking to is Ensign Darrin of the United States Navy."

"Take the wheel, Mr. Darrin," replied the youthful skipper, with a grin, while Joe, halfway up the engine-room steps, took in the scene. "I heard Mr. Darrin introduced merely as 'mister,'" Halstead explained to the other officers. "I thought he was either an Army man, or some civilian friend who had come along."

Skipper Tom Halstead then went below to his stateroom, while observant Joe Dawson noted that Darrin handled the wheel with skill.

"Shall I give you a little more speed, Mr. Darrin?" called Joe softly.

"I'm only a guest," Dave replied. "Mr. Overton is in command here."

"Thank you, Engineer, but, as we're only cruising I believe our best move will be to stick to Captain Foster's nine-mile order," Hal replied, nodding to Joe.

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 b.u.t.ts 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 sh.o.r.e, 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.