hurried because he hardly knew what to make of the restless actions of Domino. The animal seemed to be dancing up and down as though he had stirred up a hornet's nest, and the little insects were charging his exposed legs.

No sooner was Bob in the saddle than the horse gave a shrill neigh, and dashed off like a crazy creature. Indeed, a less experienced rider than Bob would have been instantly thrown by the sudden and unexpected move, something that Domino had never been known to attempt before.

Frank looked up in astonishment. His practiced eye told him in an instant that the sudden violent dash had not been engineered in the least by his chum; but was altogether the result of fright on the part of Domino. Why, the big and powerful black acted as though he had gone wild, jumping madly about, now fairly flying off to one side, only to whirl and dance and leap high in the air, until every one within seeing distance was staring at the strange spectacle. And this, too, in a town where bucking broncos were a common sight.

Frank had gained his saddle, and was chasing after his friend, but just then the black had taken a notion to run, and apparently nothing in that country could overtake him while his present savage mood held out.

"What ails the beast?" Frank asked himself, as he drew rein and watched the other passing beyond range of his vision among the stunted mesquites outside of the edge of the town. "He acts like a locoed horse; but there isn't a bit of the poison weed growing within twenty miles of here. And why was Peg Grant standing on the stoop of the tavern grinning as I rode past? Can he have had a hand in this sudden crazy spell of the black? Spanish Joe knows all the tricks of putting a thorn under a saddle, that will stab the horse when the rider mounts. Is that the trouble now? If it is then it's lucky my chum knows as much as he does about managing a horse, or he would never come back alive from that mad ride. And all I can do is to sit here, wait for his return, and watch Peg Grant and his cronies!"

CHAPTER III

OLD HANK COOMBS BEARS A MESSAGE

If there was one thing Bob could do well, it was to ride. Born in Kentucky, where horses take a leading part in the education of most boys, Bob had always spent a good part of his time in the saddle.

Hence, when he came out here to the plains, the cowboys of the ranch found that, in his own way, he was well versed in managing the fine black horse he brought along with him.

Of course there were dozens of tricks which these daring riders of the plains could show the tenderfoot from the South; but when it came down to hard riding Bob was able to hold his own.

When his powerful horse bolted in such a strange fashion Bob simply kept his seat, and tried to soothe Domino by soft words. For once the remedy failed to produce any immediate effect. The animal seemed fairly wild, and tore along over the open country like mad.

"He never acted like this before in all his life," thought Bob, as he found considerable difficulty in keeping his saddle, such were the sudden whirls the black made in his erratic course.

But although he had by no means learned all the things known to old cowmen, Bob had picked up quite a few points since arriving at the ranch. He had even heard of a mean trick practiced by revengeful Mexicans, and others, when they wished to place a rival's life in danger.

"Something has happened to him since we went into that store," Bob said again and again, as he puzzled his wits to hit upon an explanation for the animal's remarkable antics. "Now, what could it have been? Would any fellow be so mean as to fasten some of those prickly sand burrs under his tail? Or perhaps it's a poison thorn under the saddle!"

This last idea seemed to strike him as pretty near the truth. He began to investigate as well as he was able during the rushing of the runaway horse. When, in pursuing his investigations, he ran his hand under the flap of the saddle, he could feel the horse start afresh, and his queer actions seemed worse than ever.

"That's just what it is, as sure as anything!" Bob declared, his whole frame quivering with indignation at the thought of anyone being so cruel and treacherous; "but how in the wide world am I going to get at the thing?"

His first impulse was to ease the strain all he could by removing his weight from the point where he believed the thorn to have been hidden. This he did by leaning forward after the manner of a clever jockey in a race, throwing pretty much all his body upon the shoulders and neck of the horse.

Then he again began to speak soothingly in the ear of Domino. By degrees the horse seemed to slacken his wild pace.

Encouraged by this fact, Bob continued the treatment. It appeared as though the intelligent animal must comprehend what was wanted, for, although evidently still in more or less pain, he gradually ceased his runaway gait, until, finally, at the command of "whoa!" Domino came to a complete stop.

Bob was on the ground immediately. His horse was trembling with excitement and other causes. Bob continued to pat him gently, and speak soothing words. All the time he was working toward the buckle of the band by means of which the saddle was held firmly on the beast's back.

Once he had a grip on this he made a sudden pull. Domino squirmed, and for the moment Bob feared the animal would break away.

"Easy now, old fellow; take it quiet! I'll have that saddle off in a jiffy; and see what is wrong. Softly, Domino! Good old Domino!"

While he was talking in this manner Bob was releasing the band; and, with a sudden jerk, he threw the saddle to the ground.

His quick eye detected signs of blood on the glossy back of the Kentucky horse.

"That's what it was!" he exclaimed, angrily. "A thorn of some kind, put there so that when I jumped into my seat my weight would drive it in. And I reckon, too, it would be just like the cowardly sneak to pick out one that had a poison tip! Oh! what a skunk! and how I'd like to see some of the boys at the ranch round him up! But I wonder, now could I find it? I'd like to get Frank's opinion on it."

The horse had by now ceased his mad prancing. This proved that the cause for his strange actions had been removed when Bob cast the saddle off. And it did not require a hunt of more than two minutes to discover some little object clinging to the cloth under the saddle. It was, just as Bob had suspected, a thorn with several points that were as sharp as needles, and very tough.

Bob put it away in one of his pockets. Then he once more replaced the saddle, carefully adjusting the girth so as to avoid any more pressure on the painful back of Domino than was absolutely necessary.

The horse seemed to understand his master's actions, and, although still restive, allowed Bob to mount.

Cantering along over the back trail, in half an hour Bob came in sight of his chum heading toward him.

"Well," said Frank, as they finally met, "I was beginning to get worried about you, even though I knew you could manage a horse all right. It was a lively run, I should say," as he glanced at the foam-streaked flanks of the gloss black.

"As fierce a dash as I ever want to take," answered Bob, patting his horse gently.

"Did you find out what ailed him?" asked the other.

"After I'd spent some time trying to keep from being thrown, I did."

As he said this Bob drew the thorn from his pocket, and held it before Frank, who took the vicious little thing in his hand.

"I thought so," he muttered. "That's Peg's idea of getting even with us; the coward!"

"But you don't mean to say Peg did that?" exclaimed Bob, astonished.

"Well, not with his own hand. He wouldn't know how, you see; but he had a Mexican cowboy along with him who is up to all these tricks—Spanish Joe. When we were busy in that store, he crept up and fixed this