"You know as well as I do-the water just started coming out of the hole again."

"You see anything?"

"Nothing but dark."

Doc Savage went back to the aperture in the base of the cliff from which the river spouted. He used his flashlight, which was waterproof.

"Holy cow!" Renny e.j.a.c.u.l.a.t.ed, and pointed with one of his big fists.

Doc had seen it. An arrowhead, black, more than a foot in length, and inlaid or carved into the face ofthe cliff.

"That's queer," Monk muttered. "That thing is like the smaller black arrowheads. Why don't we compare 'em?"

Doc Savage still carried the second of the two arrowheads which had been taken from the Colorados.

He produced it and held it close to the black arrowhead on the face of the cliff.

A moment later, the river stopped flowing.

DOC SAVAGE'S bronze features remained expressionless in the reflected glow from their flashlights, but the others looked startled.

"That-that arrowhead-stops the water," Long Tom said, putting amazement between his words.

"But-but how?"

"Have you a pocket knife?" Doc asked.

"Yes. But what-"

"Hold it against this arrowhead," Doc suggested.

Long Tom stared as the knife blade picked up the arrowhead. "Magnetic!"

"The small arrowhead is made of lodestone, which is naturally magnetic," the bronze man explained quietly. "Behind the large arrowhead on the cliff face is doubtless some kind of a trip which is operated magnetically by the smaller arrowhead, and that in turn shuts off the water by a mechanical arrangement."

"But what-"

The river began flowing again, like a great fire hydrant that had suddenly been turned on.

"Which answers my question," Long Tom said. "The thing shuts off for only so long at a time-just long enough to permit a person to enter or leave."

Monk emitted an angry rumble.

"Shut her off again!" he said. "I'm willing to give that hole another whirl."

They shut off the water, then raced to the hole, sank to all fours, and began climbing.

"Come on, Habeas!" Monk called, and Ham said: "Chemistry, step on it!"

Chapter XIII. THROUGH THE MISTS.

THE walls were dark, smooth, and shone with wetness which threw back the white spray of their flashlights in jeweled glitter. The slant was about the same as a stairway, although the steps were higher, about two feet, and of nearly the same depth. The steps and the tunnel wall were not of the same stone as the cliff, but of harder flintlike stone blocks joined together so that the cracks were hardly noticeable.

It was perhaps forty feet up to a platform of stone onto which they could climb clear of the water channel.

The platform was wet with spray, slick, and Long Tom fell down. He said several words which the others were not aware he knew.

"Tsk, tsk," Monk said. "Such language!"Monk then made an involuntary dash for the far side of the platform, for water fell down the shaft with a deafening roar.

There were steps leading upward.

They put their heads together and screamed at each other. "We will go up," Doc Savage said.

The stairway followed above the roaring stream for some distance, then veered sharply to the left, and they were in a tunnel. The walls were not lined; they were natural stone.

Habeas Corpus, the pig, made tapping sounds as he walked. Chemistry was noiseless, although he chattered fearfully once.

Their flashlights poked out cones that seemed made of thin cotton, an effect due to the presence of something like fog. The vapor puzzled Monk, particularly after they got farther along the pa.s.sage.

"I thought this stuff was spray from the water," Monk grumbled. "It don't seem to be. I wonder-"

He went silent, for Ruth Colorado was coming toward them. Her form was vague in this mist; she was within three arm lengths before they saw her. It was eerie. She seemed to materialize before them like a supernatural body.

"Go back," she said. "There is a black arrowhead on the wall at the head of the water tunnel, so that you can stop the flow of the water."

She spoke in a low voice. There was tense earnestness in her manner. And when she looked at Doc Savage, there was a warm light in her eyes.

Ham, in the background, kicked Monk on the shin, breathed, "She likes him!" And Monk, because the girl was very pretty and he had been harboring some ideas, turned around and returned the kick to Ham's shin, with interest. Ham's yip of pain echoed faintly.

"Where is your brother?" Doc asked gently.

"He has gone on, and will return with-with the others," the girl said rapidly. "He left me to watch and give an alarm if you followed. I-well-I know you are not our enemy, so here I- Please go. Please!"

Doc Savage was uncomfortable. "As a matter of fact, it had not occurred to us to turn back."

"Why? Surely you came here for no reason except curiosity. It is curiosity, isn't it?"

"Partially-"

"Go away and forget all this-mystery," Ruth Colorado urged. She reached out and gripped both the bronze man's arms. "The price you'll pay for learning the secret is too great. So great that I-I don't want it to happen to you."

There was a pounding earnestness in her voice that caused Long Tom to moisten his lips, and Renny to open and close his big fists nervously.

Doc said: "Curiosity isn't the only reason we are here. We are fighting Spad Ames. We can fight him more effectively if we know what he is after-if we know what is behind all this mystery."

Ruth Colorado searched the bronze man's face, said finally: "I am trying to help you.""We know that," Doc Savage said gently. "And that is why we are going back."

"Going back!" Renny barked. "But Doc-"

The big-fisted engineer never got his argument finished. For suddenly, like smoke from a campfire, the mists thickened.

And it began to get cold.

Ruth Colorado put back her head and shrieked: "Don't kill us! I am with them!" Then, apparently realizing she had cried out in English, she shifted to the language which Doc had never heard before, and called out shrilly.

It was getting colder with incredible swiftness.

"For the love of Eskimos!" Monk yelled. "What kind of a place is this?"

Doc whirled, rapped: "Back toward the river! We may be able to make-"

"Wait!" The girl was gripping his arm again. "Stay here! They will not-I am with you. You are safe as long-as long as you do not let me go."

Out of the mists came her brother's voice. He spoke English.

"You are a fool, my sister," Mark Colorado said. "You are saving their lives. We will have them on our hands, a perpetual source of trouble."

The girl put her chin up, said nothing.

It stopped getting colder. The fog thinned a little. There was movement in the mists, beyond range of their flashlights.

"Do not resist them," the girl said.

Monk took two large rocks out of his pockets, said: "This won't be resistance. It'll be a ma.s.sacre!"

It wasn't exactly a ma.s.sacre, but it was brisk while it lasted. The mists suddenly thickened, and forms came flying out of them, long and grotesque forms that hardly seemed human in the strange vapor. Monk whooped, dived to meet the first one. He drove a fist. The attacker dodged expertly, took Monk around the waist, slammed him to the tunnel floor.

Two figures charged upon Doc Savage. The bronze man side-stepped. He made no effort to strike out, being interested in hearing what kind of weapons they had, and in what the a.s.sailants looked like.

The attackers were naked, except for short trousers that fitted as snugly as tights. All had remarkably white hair. And their bodies, lithe and corded with rippling strength, were greased.

Doc laid hold of one of them. The fellow was as slick as a catfish. Doc grabbed again, this time for the white-haired a.s.sailant's hand. He got it. The hand was covered with sand, so that it would hold a grip.

Clutching the fellow by the hand, Doc swung him, knocked another down.

Monk had gotten up, was chasing a man, grabbing him again and again, only to have the greased body slide out of his angry fingers.

Ham was probably being most sensible of all. He danced back, managed to unlimber his sword cane,and began p.r.i.c.king each attacker to rush him. He made no effort to cut off heads or arms or run victims through-he merely broke skin with the tip of the blade, which was coated with a chemical that would cause quick unconsciousness.

Mark Colorado called out loudly, speaking the strange dialect. He must have called for help, because there was an overwhelming rush of seminaked, white-haired men.

As Monk explained it later, he got along all right until he was fighting at least thirty men at once, and he might have been all right then, except that he kicked a greasy foe, got grease on his foot, then slipped and fell when he tried to stand on the foot.

This was probably a slight exaggeration. They were only fighting about forty opponents, all told, when they were overcome.

Chapter XIV. MIST MEN.

AFTER he had opened his eyes, Doc Savage lay for some time without moving, although all his sensations were of motion-turning over and over and around and around with slow dizzy speed, and in s.p.a.ce-while actually he was lying still. The dizziness went partly away. He moved, first his arms and then his legs, and learned he was not tied. After that, he was quiet again, shifting his eyes and listening.

He got the impression he was in a very small place.

It was dark. The darkness had a blue-black quality. Once, the bronze man thought there were small lights swimming overhead, but he touched his eyes with his fingers and discovered it was only the result of being struck on the head-the same visual phenomena occurring when a fingertip is pressed to the side of the eyeball. He did not know exactly what he had been struck with. Seven or eight semi-naked a.s.sailants had been holding him at the time. A rock, probably.

There was breathing near him; then some one cleared a throat. Unconscious people do not clear throats; they only cough.

"Monk," Doc said.

"How long you been conscious?" Monk asked.

"A few moments. And you?"

"Longer. I think they beat on your head a while after they got you down. I seem to remember that."

"Any idea where we are?"

"Some place I'll bet we'll wish we weren't," Monk said. "No. Last I remember, we are going around and around with those guys in the tunnel."

Monk thought of something, called, "Habeas! Habeas Corpus!"

Somewhere near, but not in their tiny inclosure, the pig began squealing. Chemistry, the chimp, emitted some forceful opinions in his own language.

Doc Savage lifted up. His head b.u.mped the top. He explored with his hands, found stout wooden poles.

He also located Ham, Long Tom and Renny.

"They hurt?" Monk asked."Not bad, apparently. They haven't revived yet."

The pig and the chimp continued to make a noise, and this drew attention. Footsteps approached, and there were low, guttural voices. Yellow light suddenly flooded Doc and the others.

They were in a cage made of tough wooden bars-the bars were ocotillo, the desert cactus shrub also called coach whip and devil's walking stick-that were almost as tough as iron. A curtain covered the thing, and this had been lifted.

The men outside were seminaked, white-haired; and they carried a few torches which gave off gory red light and strings of smoke which mixed with the darkness and the smoky-looking air.

Mark Colorado had removed his civilized clothing. He wore, like the others, nothing except an article that resembled bathing trunks.

Mark Colorado leaned against the bars, holding a rock so its red light flickered over them.