"I don't see how," Frank murmured, scanning the terrain. "There's no place for him and his horse to hide."
The cliff walls on either side were bare and precipitous. With the moon almost directly overhead, the snow-covered floor of the canyon was revealed with brilliant clarity. The narrow riverbanks were barren of brush. Aside from a few scattered rocks -none big enough to afford cover-nothing intervened between the boys and the frozen waterfall.
"Well, he must be here somewhere," Joe said edgily. "His tracks will give us the answer."
Frank agreed. The boys dismounted and moved forward cautiously, leading -their horses. Moonlight wrapped the scene in eerie loneliness. The boys kept their eyes and ears alert. Gradually they became aware of another sound-the muted roar of falling water, still flowing behind the glacier-like formation.
The sound became louder as they neared the cataract. The majestic ice curtain glittered in the moonlight.
It was fringed with great, jagged blue-white spears that hung down like stalactites.
"I don't get it," Joe muttered. "Al's tracks lead straight toward the waterfall!"
As they proceeded, Frank took out his flashlight, and switched it on. He gave a cry of surprise.
"Joe! He must have gone under the waterfall!"
At the base of the cliff was a dark open space yawning between the curve of the falls and the rock face!
It was large enough to admit a horse and rider. The boys moved closer for a better look and Frank probed the darkness with his flashlight.
"Look! There's an opening in the cliff wall!" Joe exclaimed. "It must be a tunnel!"
"Or maybe just a blind cavern," Frank said, switching off his flashlight. "Big Al could be waiting for us in there!"
After a whispered conference, Frank groped his way behind the cataract. When he reached the opening in the cliff he quickly snapped on his flashlight again for a more leisurely examination.
Presently he came back and reported to Joe. "It's a tunnel, all right. No telling how far it goes -or where."
"No sign of Big Al?" Joe questioned.
"Not in person, but there are wet tracks."
The two horses balked a bit as the boys took their bridles and attempted to lead them into the dark space behind the icy falls. Joe's animal, which was in the lead, whinnied and reared when it felt the splattering spray, but it soon calmed under Joe's reassuring hand.
Inside the tunnel mouth the passage widened, giving the boys room to mount. Frank and Joe rode slowly forward, with Joe, in the lead, shining his flashlight.
After several hundred yards the passage widened and the boys were able to ride side by side.
"Must have been the bed of an old underground stream," Frank guessed. "See how smooth the walls are worn."
Joe nodded. "We'd better speed up before Big Al gets too far ahead."
Urging their horses to a faster pace, they pushed on through the tunnel. At intervals the boys stopped and listened, hoping to catch some sound of their quarry. The fourth time they halted, a faint echoing sound of horse's hoofs on rock reached their ears from somewhere ahead.
"We must be getting closer!" Joe said tensely.
Just how close was difficult to judge, since the enclosed passage with its smooth, hard walls might carry the sound almost any distance. The boys rode on steadily. When they paused to listen once more, the hoofbeats were no longer audible. But twenty minutes later Joe thought he could detect them again.
"He may be far ahead of us," said Frank. "Sound can be pretty tricky in here."
As the brothers continued along the tunnel, the chill, dank atmosphere gradually became warmer. Frank and Joe unzipped their heavy windbreakers.
After a while it became necessary to rest the horses. The Hardys did not dare pause too long for fear of losing Big Al completely, and soon went on.
The tunnel turned and twisted. The horses were nervous at first about proceeding, but gradually became accustomed to the experience.
"It seems as if we've been traveling for hours," said Frank. Presently he snapped on his flashlight to glance at his wristwatch. To his amazement, it was almost three-thirty in the morning! "Whew! Do you realize the night's almost over, Joe?"
"I sure do. The horses are bushed."
Gradually the boys became aware that the tunnel was sloping upward. The horses began to pant and labor from the steepness of the incline, and the Hardys had to rest them more frequently.
"It's getting colder in here," Joe said with a sudden shiver. Both boys zipped up their jackets.
"We must be getting close to the surface," Frank said hopefully.
Sometime later he was about to turn on his flashlight again when he paused. "Hey! The tunnel's not so dark as it has been-or am I imagining things?"
"You're right!" Joe replied, with rising excitement. "I'll keep my flashlight off for a while."
Soon the boys could feel cold air on their faces. The tunnel was lightening every moment, and presently a gray glimmer of daylight showed ahead. With joyful cries of relief, Frank and Joe urged their horses forward.
In a minute or so, they had emerged onto a snow-covered mountainside. Rocks, scattered trees, and slopes all around them were bathed in the ghostly light of dawn. The Hardys leaped from their horses, stretched their tired muscles, and inhaled the fresh air deeply. Then they looked around and assessed their situation.
"There are Big Al's tracks," Joe said, pointing them out.
Frank nodded. "Fairly fresh, too-but he could be a good distance ahead of us."
"Any idea where we are, Frank?"
"Not much, except that we've come clear through the mountain." Frank grinned wryly. "I'm famished, Joe. How about you?"
"Same here! Think we can take time to eat?"
"May as well," Frank decided. "No telling how long we'll be on the trail. Lucky we didn't unpack."
The boys fed their horses, built a small fire, and had breakfast. Then they swung back into the saddles and resumed their pursuit of the outlaw. His tracks led upward onto a beaten trail winding along the mountainside.
When they reached the path, Frank reined in his mount and glanced toward a high, jutting rock formation farther up the mountain. "Know something, Joe?" he remarked. "I'll bet this is a continuation of Ambush Trail."
Joe snapped his fingers. "You're right! I remember seeing that rocky outcrop way in the distance, just before we fell into the river!"
"If this is Ambush Trail," Frank went on, "Big Al must be heading for their hideout on Windy Peak."
"That figures," Joe agreed. "He thinks he's shaken us by going through the tunnel."
The boys continued their pursuit throughout the morning. Around noontime, Big Al's tracks left the well-defined path and disappeared upward among the higher rocks and brush.
Joe groaned at the sight. "Good grief! How can we tackle that kind of ground when our horses are exhausted already?"
Frank looked thoughtful as they slouched in their saddles and studied the terrain. "Maybe there's no need to, Joe. I have a hunch this could be a dodge to throw us off."
"You could be right," Joe said, brightening. "If Big Al's heading for Windy Peak, he'll probably have to come back to the trail eventually."
After talking the matter over, the Hardys decided to halt for lunch and a rest. Two hours later, feeling refreshed, they hit the trail again.
It was late in the afternoon when the boys sighted the outlaw's tracks once more, leading from the slope back down to the trail.
"Your hunch paid off, Frank!" Joe exclaimed. "These tracks look pretty fresh, tool"
Encouraged, the boys pressed forward with new energy. A mile farther on, the trail forked. One branch struck sharply upward. The other followed a more winding course along the curve of the mountainside.
To their left stretched a shallow box canyon.
Frank and Joe took the lower trail, since the prints showed that Big Al had gone that way. Gradually the path became little more than a rocky ledge, with frequent sharp turns and a sheer drop-off along the outer edge. The Hardys rode single file, with Joe in the lead.
Suddenly a pebble clattered down from a rock jutting out just above their heads. Frank shot a quick glance upward. "Look out, Joe!" he yelled.
A rope with a wide circling noose was snaking down toward his brother's head!
Frank's warning came an instant too late. The noose settled over Joe's shoulders and jerked tight, nearly yanking him from the saddle.
Frank spurred forward, white with terror. Someone hidden on the ledge above them was trying to drop Joe over the precipice! Frank managed to grab the taut rope just in time. Almost at the same instant, the unseen enemy let go of it. Joe would have gone over the brink, but Frank's quick jerk on the rope pulled his brother back from the edge, and Joe dropped heavily onto the trail. Unhurt, he struggled to his feet and began extricating himself from the noose. In moments he was free.
"There goes the rat!" Frank yelled as a figure burst from the ledge above and scrambled rapidly along the slope.
Big Al!
Instantly Joe was back in the saddle. The Hardys spurred forward in hot pursuit. The outlaw's course was roughly parallel to the trail. Suddenly Big Al checked his stride long enough to send a large rock rumbling down the slope.
"Hold it, Frank!" Joe warned.
Both boys yanked their horses to a rearing, whinnying halt in the nick of time! A split second later the rock crashed onto the trail just ahead, rolled to the edge, and went over.
The animals snorted with fear and stood trembling. Frank and Joe barely managed to spur them into motion again. Big Al was lost to view behind a clump of brush and jagged outcropping.
The trail ahead bent sharply around a projecting shoulder of the mountainside. Joe caught a quick glimpse of Big Al outlined against the sky as he rounded the slope. Then he disappeared.
The boys slowed their mounts to negotiate the dangerous hairpin curve of the ledge. As they came around to the opposite side of the shoulder, Joe reined in and signaled Frank to halt. Ahead stood Big Al's riderless horse. The Hardys dismounted to scout the situation.
"Where has he gone?" Frank asked tensely.
"Search me," Joe replied, looking around.
Just past the outlaw's horse the trail petered out and the terrain sloped upward in a jumble of giant rocks.
Beyond them a huge boulder stood poised straight up like a pinnacle.
"He must be holed up among those rocks," Frank said. "Probably waiting for us!"
He had hardly finished speaking when Joe clutched his brother's arm and pointed. "Look! There he is!"
Big Al had suddenly appeared, clawing his way to the very top of the jutting boulder!
"He's trapped!" Frank cried out triumphantly. "Let's get him!"
CHAPTER XVI.
Cliff Hideaway "YOU'LL never take me alive!" screamed Big Al.
He had reached the top of the huge boulder and now stood waving his arms against the leaden sky. The outlaw was jumping around as though half-crazed.
"Try to get me!" he challenged.
As Frank and Joe sped into the jumble of rocks, they lost sight of their quarry momentarily. They could hear Big Al still yelling, then suddenly there was silence.
"Wonder what happened?" Joe panted. "Did-"
He was interrupted by a long-drawn-out scream which gradually trailed off. Then there was silence.
Dashing from the rocks, the boys came around a corner. Before them was the huge boulder.
"He's gone!" Joe panted.
"But where?"
There was no place for Big Al to have run except down the rocky trail on which the boys had been.
"He must have jumped over the edge!" Joe yelled. The Hardys ran to it. They could see most of the canyon floor below them. There was no sign of a body.
"He must have gone down!" Frank said, puzzled. "But where is he?"
The boys looked closely again in the waning light. There was no one in sight.
"I wonder-" Joe said slowly. "Even if Big Al did go over the side, he may have known a safe way to slide to the bottom, and there might be some hiding place-"
Frank agreed. "Big Al's pretty tricky. He could have figured out some way to escape."
As the light failed, the brothers strained their eyes to peer into the darkness, but could detect no niche, crevice, or cave in which to hide.
"Well," Frank murmured at last, "there isn't much we can do tonight. I sure hate to think Big Al is roaming around here loose."