Part 15 (1/2)

”The planes and the rest of the hangar look all right,” he said. ”It's just us and the sedan that's green. Why is that?”

”It's because you walked through the grayish fog, that came from those cylinders you threw out of the window,” Doc explained. ”The car was driven through the fog, too.”

”Velvet and Biff also drove through it,” Monk e.j.a.c.u.l.a.t.ed.

”Which should make it simple for us to find them,” Doc said dryly. ”Touring cars are scarce this cold day.

The chances that more than one drove past that skysc.r.a.per while the fog was in the street, are very slim indeed. Look for a touring car which shows green under the ultra-violet light.”

It was not necessary for Doc Savage to go into a detailed recitation concerning ultra-violet light. His men had seen it in operation before. Doc used it a great deal.

Ultra-violet light, being outside the visible spectrum, does not register on the retina of the eye; for that reason it is sometimes called ”black light.”

Certain substances, however, behave strangely when exposed to ultra-violet light. They fluoresce, or glow, in unearthly hues. Ordinary vaseline and aspirin are two substances which behave thus.

The chemicals which composed Doc's strange fog were another. He had developed the stuff by careful experimenting. Its propensity for this glowing phenomena was extremely p.r.o.nounced.

The tiny quant.i.ties of the grayish vapor, deposited on bodies moving through it-such as walking men and moving automobiles-was sufficient to glow in a very brilliant fas.h.i.+on.

Doc Savage pressed a b.u.t.ton. This set an electric motor in operation, and opened the vast rear doors. The hangar floor sloped down into the river. There was a small film of ice on the water. The first plane to enter-the great tri-motored high-speed amphibian, with Renny at the controls-broke the ice.

In rapid succession the planes took the air. There was a craft for each man.

Every s.h.i.+p was fitted with a powerful ultra-violet light projector. These had been installed for a long time. This was not the first time Doc had used ultra-violet light. It was, however, his initial experiment in tracing men who had merely walked through a fog of Doc's own making. The six planes scattered to the northward-Velvet and Biff had driven north.

The projectors of ultra-violet light were turned on. These were of Doc's own design, and extremely powerful.

The s.h.i.+ps flew low. At times they literally banked around skysc.r.a.pers, spires.

Monk, spotting a car which glowed green below, all but collided with a high building. He flew down into the canyon of a street, frightening stenographers and the inevitable clouds of pigeons which swarmed around the rooftops.

”Blast it!” Monk grumbled, and zoomed upward again.

The car he had discovered was a convertible. No doubt it had chanced to drive through the vapors surrounding Doc's skysc.r.a.per headquarters.

The hunt worked steadily northward.

EACH of Doc's five men was flying a different plane. Doc himself, however, had taken up the strangest crate of the lot. At first glance this seemed merely an auto-gyro.

An airman would have immediately noticed something unusual about the craft, however. For one thing, the taila.s.sembly had no control surfaces. There was merely a fishtail effect. The two stubby wings usually supplied on auto-gyros were missing.

Doc's craft was a true-gyro. In the hands of a pilot sufficiently skilled, it could land on a table top, and take off from the same point.

Doc Savage sent his unusual s.h.i.+p ahead of the others. He selected one of the main arterial streets, and traced it. If Velvet and Biff had parked their car downtown, one of Doc's men would probably locate it. Doc himself hoped to overhaul the pair if they had kept driving.

Doc saw no sign of a touring which showed a weird color under the powerful ultra-violet light. He widened the sphere of his search. Touring cars were very scarce.

For fully an hour they hunted.

The planes were fitted with radio-telephone transmitters and receivers. These sets were supplied with Doc's version of what is popularly known as ”voice-scramblers.” These contrivances distorted voice sounds at the transmitting end, and straightened them out at the receiver.

Any one tuning in on Doc's interplane conversation would not have been able to understand a word of it.

By radio, Doc ascertained his men had found nothing.

”Biff and Velvet have done one of two things,” Doc decided. ”Either they drove their car into a garage, or they hurried straight out of town.”

”They sure don't seem to be on the streets below,” Monk agreed. He spoke as if they were in the same room, instead of being widely separated in the frosty sky.

”Let's look the airports over,” Doc suggested.

”Maybe they lit out along some country highway,” Renny's thunderous voice offered.

”In that case, they will be easy to catch,” Doc told him. ”The storm last night blocked the roads with snow.

They have not yet been cleared.”

The six planes whipped away in various directions, each seeking an airport.

It was Doc who sighted the curtained touring car. He discovered it near a big airport in New Jersey. It was headed toward town, not away from it.

Doc swung his gyro along above the car, matching the car's speed. At the same time he descended swiftly.

The gyro motor was efficiently m.u.f.fled. It was unlikely that those in the car would hear it.

Something over which Doc had no control betrayed his presence. The men in the coach saw the shadow which his plane cast on the snow.

The rapid approach of the shadow alarmed them. They thrust heads out, looked upward, and saw Doc.

Gun muzzles sprouted from the car curtains. They lipped flame.

DOC jerked his head inside the gyro. Bullets snapped at the spinning wing-vanes. Slugs drummed fiercely against the underside of the fuselage. They hammered staccato thunder. The concussions were so regular that Doc knew one of the weapons below was a machine gun.

The gyro cabin was fitted with a thin, very tough alloy armor. A high-powered rifle bullet, hitting squarely, would have penetrated it. The armor was effective against the weapons below, however.

Doc s.h.i.+fted the lever which controlled his forward speed. He shot ahead of the touring car. Then he touched another lever. This caused a mechanism to click.Hollow tubes projected from the gyro hull. These spat slender aero bombs. Striking the snow-covered pavement ahead of the touring car, the bombs turned into great mushrooms of bilious-colored smoke.

The car plunged into the vapor. The driver had locked the brakes, and the car slewed from side to side.

The automobile skidded off the pavement, plowing up snow. It came to a stop, half buried in the flake-filled ditch.

Doc dropped his gyro near the machine. The snow was over his knees. He plunged through it, got a look inside the touring car, and his haste evaporated.

The girl, Tip Galligan, was not in the machine. Nor were Velvet and Biff present.

It was a villainous-looking crew which the touring car bore. They numbered seven. Small-time crook was stamped on the face of every man.