from tree to tree, for he had not the least idea when he would run across a guard.  The whistling ceased, but the marshal was now so near that he could follow the original direction without much trouble.  In a few moments he might distinguish the sound of voices.  If there were two or three men in the camp he might be able to surprise them and make his arrest.  If the outlaws were many, at least he could lie low near the camp and perhaps learn the plans of the gang.  He worked his way forward more and more carefully.  At one place he thought a shadowy figure slipped through the brush a short distance away.  He poised his gun, but lowered it again after a moment’s thought.  It must have been a stir of shadows.  No human being could move so swiftly or so noiselessly.

Nevertheless the sight gave him such a start that he proceeded with even greater caution.  He was crouched close to the ground.  Every inch of it he scanned carefully before he set down a foot, fearful of the cracking of a fallen twig.  Like most men when they hunt, he began to feel that something followed him.  He tried to argue the thought out of his brain, but it persisted, and grew stronger.  Half a dozen times he whirled suddenly with his revolver poised.  At last he heard a stamp which could come from nothing but the hoof of a horse.  The sound dispelled his fears.  In another moment he would be in sight of the camp.

“Do you figger you’ll find it?” asked a quiet voice behind him.

He turned and looked into the steady muzzle of a Colt.  Behind that revolver was a thin, handsome face with a lock of jet black hair falling over the forehead.  Calder knew men, and now he felt a strange absence of any desire to attempt a gun-play.

“I was just taking a stroll through the willows,” he said, with a mighty attempt at carelessness.

“Oh,” said the other.  “It appeared to me you was sort of huntin’ for something.  You was headed straight for my hoss.”

Calder strove to find some way out.  He could not.  There was no waver in the hand that held that black gun.  The brown eyes were decidedly discouraging to any attempt at a surprise.  He felt helpless for the first time in his career.

“Go over to him, Bart,” said the gentle voice of the stranger.  “Stand fast!”

The last two words, directed to Calder came, with a metallic hardness, for the marshal started as a great black dog slipped from behind a tree and slunk towards him.  This was the shadow which moved more swiftly and noiselessly than a human being.

“Keep back that damned wolf,” he said desperately.

“He ain’t goin’ to hurt you,” said the calm voice.  “Jest toss your gun to the ground.”

There was nothing else for it.  Calder dropped his weapon with the butt towards Whistling Dan.

“Bring it here, Bart,” said the latter.

The big animal lowered his head, still keeping his green eyes upon Calder, took up the revolver in his white fangs, and glided back to his master.