"Three?"

Doc Savage said sharply.

"Yeah. The third one just flew in from the south. Guess it's the plane carrying Spad Ames' guns and bombs and stuff. Probably they arranged a meeting by radio."

Doc Savage went forward grimly.

"This is what we wanted-to find Renny," he said grimly. "We'll bring those planes down as fast as we can."

Monk glanced downward and shuddered.

"They won't like that very well," he surmised.

IF a great mult.i.tude of needles, made of stone and of lengths ranging from five hundred to four or five thousand feet in length, had been placed together in a great bundle with the points uppermost, the result would have been a fair imitation of what was below. Directly ahead, one of the great cracks seemed half filled with fog, which was a little queer. Fog was unusual in this desert.

Ham looked a little queer, and without a word, got a parachute and put it on.

"Good idea," Doc Savage said, and they all strapped 'chute harness to themselves, and upon the two prisoners.

The bronze man took over the controls, pulled the big ship into a climb. The three planes ahead had slowed, for the plane bearing Renny and the weapons was obviously a slow craft.

A few minutes later, the three Spad Ames' planes began circling.

"Looks like they're fixin' to land," Monk said.Doc nodded. He put his own ship into a long dive, came in a long moaning comet-rush out of the afternoon haze. If there was a landing spot down there below, he intended to disable the other planes with the gas that would stop their motors, and follow down the one which carried Renny.

They saw Doc's ship. He had expected that. He had expected the ships to bank sharply, trying to get into positions for men in the cabins to use machine guns. He kept diving. There was not much chance that they would do damage, for both windows and fuselage of his plane would stop ordinary rifle and machine-gun slugs.

What he had not expected was Ham's sudden howl from back in the plane cabin.

"Ham! Watch out!"

Doc twisted. He was in time to see Mark Colorado heave up, and with his bound feet, kick the dapper Ham head over heels. Monk was already on the floor, where he had been knocked.

It was impossible for Doc to leave the controls. They were screaming toward the other three planes; there was every chance of collision.

Long Tom was on his knees at the rear, working over the engine-stopping gas containers.

Mark Colorado dived for the plane door. He had freed his hands somehow, but his ankles were still bound. The door, a siding type, could be opened when the craft was in flight. Mark Colorado wrenched it back, fell out.

He was desperate, he had a parachute, and he took a big chance. He managed to fall onto the wing-the door was directly over the wing-so that he hooked his hands over the leading edge.

He clung there until, with his free hand, he worked his parachute loose and hurled it into the propeller.

Twisting at terrific speed, the propeller knocked itself into a complex knot.

Mark Colorado lay on the wing. Doc Savage, from the c.o.c.kpit, could see the man's strangely blue eyes looking at him steadily.

The three Spad Ames' ships were above now. Monk-he had both arms wrapped about his midriff where he had been kicked-staggered to the c.o.c.kpit.

"Fine stuff!" he gasped. "Those guys can fly rings around us now."

That was true. With only one motor, any one of the three planes above was faster. Men were wrenching the windows open and leaning out, braced against the rip of pa.s.sing air, holding high-explosive grenades ready for use.

Ruth Colorado came forward, dragging herself by her arms, for her ankles were bound.

"You see that canyon?" She pointed.

"It's narrow," Doc said grimly.

"Very narrow. But you may be able to land in the bottom. It is sand, fairly smooth."

Doc glanced at the great crack in the needled wilderness of stone. He nodded, said: "We will try it."

"That is where Spad Ames crashed when he first came," Ruth Colorado said. "So be careful."

Chapter XI. STRANGE CANYON.

THE sand was not level. It was b.u.mpy. The plane made sounds somewhat like a big drum after the wheels touched; then it stopped.

Monk dived through the open door of the ship, landed upon Mark Colorado, and yelled: "I'm gonna turn this guy inside out! Ruin our propeller, will he!"

There was a ripping explosion, a geyser of sand a few yards distant. They were dropping grenades from above. Three more exploded close together on the canyon side, and a shower of rock came jumping down, the larger fragments out-distancing the smaller. Several of them were the size of automobiles.

Monk scooped up Mark Colorado and rushed with him to safety.

"I oughta leave you there for rocks to roll on," Monk declared unreasonably.

Doc Savage shouldered the girl, and ran. Ham and Long Tom tried to get an equipment case out of the plane, looked at the descending landslide of stone, and changed their minds. They raced clear.

The stone struck, knocking the plane about a little, bending it out of shape.

"Blast it!" Monk yelled. "We gotta get our equipment out of that ship!"

Doc Savage stared upward. He thought of the bombs which Spad Ames had told Locatella he would need. They were probably in the munitions ship, which was slanting slowly down toward the canyon.

"Run!" Doc said, and set an example.

The bomb must have been one of the new horrors of military science, a compressed oxygen-demolition bomb. Its concussion knocked them flat. They were deafened for moments, got up with nostrils leaking crimson.

In a hundred places, the blast had loosened the sheer canyon walls. Stone fell, pulling great comet trails of dust after it. Above the ringing in their ears, they could hear the rumbling grind of the slides. Under their feet, sand trembled so violently that dust began to arise from it.

They ran.

Monk, whose short legs handicapped him, began to yelp with each jump. But he did not drop Mark Colorado.

A few big boulders leaped across their path. Smaller fragments showered them. Echoes began coming through the din, sounding like battery after battery of big cannon being fired in succession.

Doc halted, and the others stopped also. Monk ceased yelping.

"You sounded like a coyote after a rabbit," Ham told Monk.

Monk let it pa.s.s. He was looking back at the spot where their plane had been standing.

The dust blew away after a while.

"How deep would you say the rock is over our plane?" Long Tom asked dryly.

"Fifty feet," Monk said.It was a conservative estimate.

MONK opened his mouth, then closed it without saying anything. Their predicament was clear enough without comment. The plane was gone. Spad Ames still prowled around overhead. They could hear his three planes moaning.

"Here's an overhang where they can't see us," Doc said.

They stood in the niche which water had worn in the side of the canyon and waited. One of the planes, flying very carefully, ventured down some distance into the canyon, searching. It climbed out again, apparently satisfied.

Doc Savage looked down at Mark Colorado. The white-haired man's face was placid, and he smiled slightly.

"You seem satisfied," Doc said.

"I am."

"Spad Ames is not your friend."

"Of course not."

"But you helped him by disabling our plane."

Mark Colorado shook his head. "You have the wrong slant on that. I have seen a little of your methods.

Enough to know you will be far harder to stop than Spad Ames."

"But why should you try to stop us?"

"You have learned that Spad Ames is after something mysterious," Mark Colorado said slowly. "The mystery has intrigued you. If you had managed to rescue your friend, Renny, up there a few minutes ago, you would not have been satisfied. You would have gone on. You are an adventurer. And because you have an amazing amount of ability, you might have-well, you might have gone through the mists, and learned about the destiny that no man shall know."

Doc Savage deliberately kept his metallic features expressionless. He was very puzzled.

"That sounds like-just words," he said. "Going through the mists. And destiny that no man shall solve the mystery. Words. Just words."

"That is because you do not understand."

Doc Savage glanced upward, listening. "You may be right, at that."

"He may be a little nuts, too," Monk said. "This thing has had a screwy twist from the first."

The planes had not gone away. They were out of sight, but all three motors were droning.

"They seem to be getting ready to land," Doc said.

Mark Colorado nodded. "They will descend farther down this canyon-probably a mile away. There is a spot at that point which is wider."

"You're helping us when you tell that," Doc said. "A few minutes ago, you were fighting us.""I am not helping you-I am fighting Spad Ames." Mark Colorado smiled again.

Doc turned to Ruth Colorado suddenly. "What do you think about this att.i.tude of your brother's?"

She had evidently been thinking about that, because her answer was prompt.

"The truth about my brother and myself is fantastic," she said. "And it is better for no one to ever know it."

DOC took off his coat, a dark gabardine garment. He ripped it into strips. With the strips, he bound both Colorados.

"Watch them," he said. "Watch them very closely."

"Where you goin'?" Monk called.

"To see about Renny."

High overhead, the eroded pinnacles of stone were tipped with the fire of afternoon sunlight, but here in the depths there was shadow. Not particularly dark shadow, once eyes had become accustomed to it, but murky enough to make the sunlight above seem blinding. Everywhere were the walls of stone, sheer and towering and causing a feeling of breathless awe.

Doc began running. He had been comparatively inactive for hours in the plane, and the exercise was welcome. The air was utterly dry and a little cold.

Noise of running water reached his ears, and soon he saw the stream that caused the sound. A small river, it poured out of the base of the canyon wall with rushing violence and a squirming cloud of spray.

It was on the opposite side of the canyon. He did not cross to investigate.

Judging from the sound, two of the planes appeared to have landed; Doc believed there was only one engine still running, although the mult.i.tude of echoes made it hard to be sure. He continued running until the canyon widened abruptly, when he slackened his pace, going very slowly, listening frequently.

Two of the planes had landed. The third was coming in, motor throttled, the pilot banking carefully between the walls of stone. The tricky air currents made balancing difficult. The plane seemed no larger than a house fly buzzing down into a rut that a big truck had made in soft yellow earth.

When the ship was down safely, it taxied over to the other two craft. A camp was apparently going to be set up. A ma.s.s of boulders lay on the canyon floor at that point, and the stream was nearby.

Guards scattered quickly, took up positions some distance from the camp, where they could cover the surroundings. They carried automatic rifles.

As soon as he saw Renny being hauled out of the last plane to land, Doc moved. He flattened in a small gully and crawled to the creek. On the way, he gathered rocks until he had his pockets filled.

He had a number of scientific gadgets on his person, devices which were compact, and which he usually carried when fooling around with trouble. He had a gas mask which doubled as a diving "lung." He inserted this between his teeth and applied the clamp to his nostrils.

The creek water was bitterly cold. Rocks in Doc's pocket held him on the bottom. He crawled along.

The current, while it did not have the bounding rush of a mountain stream, was fast. Keeping his eyes open, Doc remained in the deepest shadows as much as possible.The first time he crawled out of the water, he discovered he'd overshot his goal somewhat. Entering the stream again, he crawled back, with extreme difficulty, against the current. Then he lay on the bank, exercising rapidly to get the blue cold stiffness out of his muscles.

Spad Ames was giving loud orders.