The setting of the sun came about abruptly, due to the rising of a bank of clouds in the west simultaneous with the descent of the blazing orb.

"I don't think we're doin' the brainy thing!" said one of the men in the cab.

"n.o.body asked you!" growled Hack.

"Maybe not. But I don't get the idea of finishin' off the thing in the truck. After all the trouble we've gone to!"

"Sh-h-h!" hissed Hack. "It might hear you. This one ain't workin' so good. You know that. So the boss has decided to get rid of it. We'll bring up others for the big push on New York. d.a.m.n it! We'll have to get another headquarters."

"I hope that explosion got the bronze guy!" growled another "Dummy up!" said Hack, scowling at Long Tom. "This guy's got his ears unpinned."

"0. K., 0. K.," the other muttered. "What are we gonna do after we get rid of our load?"

"Light out for the Trapper Lake country," replied rednecked Hack.

Night clamped down blackly. Long Tom kept accurate check on their progress, and their whereabouts.

They followed the State highway for a time, then turned off. He could see the highway markers.

Long Tom made no attempt at a break. His captors kept eyes upon him all the time they were on theferry. Hands remained in gun-bulged pockets. His slightest move would have meant sudden death.

The van rolled on -- for hours, it seemed. The terrain became hilly. At almost every brook they stopped and added water to the radiator.

At last, the van halted. There was a stirring in the rear. Long Tom peered through the window.

Caldwell appeared from the after regions of the van. Ahead of him he propelled the steel-haired girl, Jean Morris.

Her wrists were handcuffed at her sides; adhesive tape crisscrossed her lips. She could only glare rage with her metallic eyes and make angry noises through her nostrils.

The pair were illuminated faintly by the backglow of the van's headlights.

Caldwell stared at Long Tom. He spat disgustedly. "Don't let this guy get away!" he warned. "He's probably been listening to you guys talk, and knows plenty."

"We ain't been talkin'," lied the red-necked Hack. Long Tom kept his pale face expressionless. In his listening, he had garnered one really important morsel of information. This gang seemed to have a headquarters in the vicinity of Trapper Lake, Michigan.

"How do we dish it out to him?" asked Hack, "Just tie him in the van cab," said Caldwell. "Two of you birds come along with me. The other two are enough to do the job."

"Sure," said Hack. "I know the spot. I was raised in this country. The place is right ahead. It'll work swell."

"It'd better," Caldwell said grimly.

The van rolled ahead, leaving CaIdwell, the steel-haired girl, and the two thugs behind. The ponderous vehicle covered perhaps two hundred yards, then angled into a disused side road.

The headlights picked out a tunnel-like hole which slanted down into the side of a hill. Some time in the past, an attempt at mining had been made here. The tunnel was rather large -- big enough for the van to be driven in.

The mumble of the engine became terrific thunder as the van entered the bore.

For the first time, Long Tom detected the vibration of something of great size moving in the van rear. The monster was apparently disturbed by the roar of the engine.

"I hope the thing don't try to get out!" Hack muttered.

"The van will hold it," grunted the other.

Long Tom tested the handcuff links uneasily. He was stronger than nine out of ten run-of-the-street men.

His muscles, however, were unequal to snapping the stout steel links.

"Gettin' uneasy, eh?" jeered Hack The fellow drew another set of handcuffs from his pocket He grasped Long Tom's leg. The electrical wizard kicked and pitched about violently. The driver cursed. His attention was distracted; the van crashed into the tunnel wall and stopped.

Both men seized Long Tom. Clubbing him with pistols, straining, grunting, they managed to link his ankle manacles to the steering-post "Let's go!" snapped Hack.

They piled out of the cab.

Long Tom heard sc.r.a.ping sounds, then saw the reddish flicker of machete. He leaned out. Although his feet were secured, he could see the two men. They were applying a match to a fuse which led into a large steel tool locker slung under the van body.

The fuse hissed, and spat sparks. The two men whirled and ran.

THE VAN motor had killed itself when the machine collided with the tunnel side, and inside the tunnel there was comparative silence, except for the noise of the running men. Somehow, to Long Tom, it was as if the receding steps were in actuality the departure of his own life-ghost.

He wrenched madly, fighting the handcuff links. The steel circiets sc.r.a.ped skin off his wrists and ankles, cut flesh, and rasped tendons. And they held him.

Back in the van interior, the monster stirred uneasily. On the faint chance that he might arouse the thing and cause it to break free, and in some manner accomplish the saving of himself, Long Tom began to yell.

"Bust out!" he shrilled. "They're trying to kill us!"

There was a violent stir, a terrific impact inside the van; then great blows.

The thing realized something sinister was under way. Either it had understood Long Tom or had sensed the danger.

Long Tom peered out of the cab, stretching as far as the handcuff links would permit. The sparking fire had crawled along the fuse until it was lost to view inside the box.

The monster's struggles caused the van body to rock slightly on the springs.

Long Tom widened his mouth to yell again. The shout, however, never came. Instead, he sealed his lips and listened.

He had caught a sound, a sound so weird as to defy description. A fantastic trilling note -- it might have been the plaintive cry of some exotic feathered thing lost in the umbrageous depths of the ancient mine.

It was the sound of Doc Savage.

"Doc!" Long Tom yelled.

The giant man of bronze came plunging down the declivitous mine tunnel, flashlight in hand. He moved the beam occasionally to avoid larger lumps of rock which had fallen from the roof of the abandoned diggings.

The bronze man wrenched at the underslung tool locker into which the fuse ran. It was of steel, heavily constructed like the rest of the van. Opening it was work for a key, or for a steel-cutting torch. Inside the van the monster struggled futilely.

Doc Savage leaped to the rear. A huge padlock secured the doors, too strong to break! He whipped to the cab and grasped the stout handcuff chain which linked Long Tom to the steering column.

Long Tom had battled that chain futilely. His best efforts had not even elongated the links. The chain parted under Doc's fingers as if it were cheap, soldered watch linkage.

Long Tom was yanked out of the cab and borne toward the tunnel mouth at a dizzy speed.

Doc Savage's flashlight funneled white, and in the incandescence, stony outthrusts of the tunnel walls cast weird, squirming shadows.

Here and there lay lumps of coal which had disintegrated from long exposure to the air. Grayish shale floored the tunnel, this still bearing depressions left upon the removal of tramway ties. Through these, the van tracks rutted deeply.

Long Tom gnawed his lips. He was holding his breath, unaware of doing so. Would the explosion come before they got out?

It did not. Doc Savage dived through the entrance, and veered to the right. In his haste he made some noise. Rocks rolled; bushes whipped.

Drawn by these sounds, from a spot at least a hundred yards distant, a powerful hand-searchlight protruded a white tongue. Doc and Long Tom were embedded in the glare. From behind the light, angry yells volleyed.

"h.e.l.l -- it's the bronze guy!" Hack howled.

Two gun muzzles, lipping flame, became like winking red eyes above the white-hot mouth of the hand searchlight. The bullets pa.s.sed Doc and Long Tom so closely that the ugly sound was not the conventional zing, but more like the snap of gla.s.s rods.

From the tunnel mouth came a great, whooping roar. The big hole spat shale, dust, and lumps of old coal.

It might have been the mouth of a gigantic cannon.

Chapter 13. THE MICHIGAN CLEW.

THE CONCUSSION of the explosive within the tunnel caused the earth to quake until Doc all but lost his balance, despite his tremendous agility.

Rubble was blown from the mouth of the tunnel with sufficient force to carry many yards; the stuff blasted in the direction of Hack and his companions.

As the hail of debris struck, the pair stopped shooting. Either a rock broke their light, or they switched it off, for its glitter vanished.

Doc Savage, with Long Tom's manacled frame across his tremendous shoulders, pitched through the night. The hill into which the tunnel penetrated was steep. There was danger of the explosion sliding its top down upon them.

The cataclysmic force of the detonation seemed to lift the entire hilltop. Great cracks split and gapedopen. Trees upset. Rocks and soil spurted upward, as explosion-gas escaped through the rents.

The hilltop settled, causing great gushes of dust. The tunnel mouth closed completely. The reverberations of the blast whooped and thumped, like unseen giants fighting each other, until they weakened away into nothingness.

The monster within the van, whatever might be its nature, certainly had perished in that blast, buried under hundreds of tons of stone, shale and earth.

A more effective tomb would be hard to conceive.

Doc Savage lowered Long Tom. By way of proof that the bronze man's earlier feat of snapping the handcuff b.links was no freak. the linkage securing Long Tom's wrists and ankles now parted easily under Doc's great corded hands.

"How'd you get here, Doc?" Long Tom demanded.

"Renny picked me up in the gyro," Doc explained. "Using the ultra-violet light, we managed to locate the van. We followed the thing, and lost sight of it when it went into the tunnel. I dropped down by parachute to see what had happened."

"The steel-haired girl was taken off the van a few hundred yards back," Long Tom offered.

With the ghostly abruptness as of a bronze specter, Doc Savage vanished into the night. He made directly for the spot from which the shots had been fired.

DUST ROLLED in choking waves. The cloud banks that had made the sunset so abrupt had gorged the sky with their sooty ma.s.s. Dust and clouds, combined, made the night very dark.

Far overhead, Doc could hear faint hissing noises. They might have been made by the wind. Actually, they were the sound of the silent motors which propelled Renny's gyro and the larger speed plane in which Johnny and the others rode. Johnny had landed and picked up Monk, Ham, and fat Griswold Rock.

Griswold Rock had not been enthusiastic about taking to the air, having admitted a fear of airplanes.

Doc Savage, using his fabulously sensitive ears and nostrils, ascertained that the gunmen had fled. He increased his speed. The fleeing pair had taken to the disused road which approached the mine mouth.

Doc, catching faint sounds of their flight, ran faster. His quarry had turned off the road into a very level field. Doc caught a faint tang of gasoline.

Out of his pocket came a small boxlike device. It was a radio transmitter-receiver, designed for an ultra degree in portability. He clicked the switches.

"Renny! Johnny!" he called.

"I'm on," Renny's thumping tones replied "Me, too," added Johnny's more scholastic voice.

"Toss out flares," Doc commanded. "I think these fellows have a plane waiting down here. There's a smell of gasoline in the air."

That this deduction was correct was quickly verified. A plane motor whooped into life out on the levelfield.

High overhead, almost against the black flanks of the clouds, a light appeared. Rivaling the sun in brightness, it bathed the earth in glittering white, causing every gra.s.s blade to stand out. It was the flare which Doc had ordered. It sank slowly, lowered by a small parachute. Its intensity seemed to increase as it eased down in the sky.

Doc caught sight of the plane. It was a low-wing cabin job, and it looked fast.

Caldwell himself was inside the gla.s.s enclosed c.o.c.kpit, handling the controls.

GIVING HIS engine no time to warm up, Caldwell fed the cylinders gas. The low-winged ship picked up its tail and scudded across the field.

In the calcium dare, Doc Savage discerned a feminine face jammed to the cabin windows. The steel-haired Jean Morris apparently was still a prisoner.

The plane vaulted off.

Above, Renny's gyro and Johnny's speed ship came spiraling down to attack.

Doc, directing the affair by radio, commanded, "Watch it, you fellows! The girl is in their plane."

His warning was hardly necessary, however. Caldwell's plane climbed with astonishing speed. To the west, clouds hung very low. The craft made for these. As it banked, Doc caught a glimpse of the license numerals in the flare glitter. He made note of the number, fixing the figures in his retentive memory.

It dived into the vapor bank and was lost to sight before it could be overhauled.

"Holy cow!" came Renny's disgusted e.j.a.c.u.l.a.t.i.o.n from the gyro. "We haven't got a chance of trailing them through these clouds."

Renny's gyro and Johnny's faster bus swung in great circles, searching. Johnny even climbed the ship above the clouds, where there was moonlight. No trace did they discern of Caldwell's aerial conveyance.

It had made an escape.