Doc banked his plane, set a course directly for the city of Washington, using not only the gyroscopic compass with which the craft was fitted, but calculating wind drift expertly.
'How they made the bomb explode in the air can be simply explained,' he told Renny at last. 'They probably put an altimeter or barometer in the bomb. The altimeter would register a change in height. All they had to do was fix an electrical contact to be closed at a given height, and — bang!'
'Bang, is right!' Monk put in, grinning.
Their plane flashed past the upraised arm of the Statue of Liberty, and sang its song of speed southward over the Jersey marshes.
Unlike the tri-motor which had been destroyed, this plane was of the latest design. It was a tri-motor craft also, but the great engines were in eggs built directly into the wings. It was what pilots call a low-wing job, with the wings attached well down on the fuselage, instead of at the top. The landing gear was retractible — folded up into the wings so as not to offer a trace of wind resistance.
It was the ultra in an airman's steed, this supercraft. And two hundred miles an hour was only its cruising speed.
No small point was the fact that the cabin was soundproof, enabling Doc and his friends to converse in ordinary tones.
The really essential portion of their equipment was loaded into the rear of the speed-ship cabin. Packed compactly in light metal containers, an alloy metal that was lighter even than wood, each carton was fitted with straps for carrying.
In a surprisingly short time they picked up the clustered buildings of Philadelphia. Doc whipped the plane past a little east of the city hall — the center of the downtown business districts.
Onward they swept, to zoom down on an airport at the outskirts of Washington.
The landing Doc made was feather-light, a sample of his wizardry with the controls. He tailed the plane about with sharp whirls of the nose motor, and taxied for the little airport administration office.
In vain did he look about for his autogyro. Ham should have left the windmill plane here, had he already arrived. But the whirligig ship was not in evidence.
An attendant, a spick-and-span dude in a white uniform, ran out to meet them.
'Didn't Ham show up here?' Monk demanded of the man.
'Who?'
'Brigadier General Theodore Marley Brooks!' Monk explained.
The airport attendant registered shock, then great embarrassment at the words. He opened his mouth to speak, but instead, excitement made him merely stutter.
'What has happened?' Doc asked in a gentle but powerful tone that compelled an instant answer.
'The airport manager is holding a man over in the field office who says his name is Brigadier General Theodore Marley Brooks,' the attendant explained.
'Holding him — why?'
'The manager is also a deputy sheriff. We got a call that this fellow had stolen an autogyro from a man named Clark Savage. So we arrested him.'
Doc nodded absently. He was clever, this unknown enemy of theirs. He had decoyed Ham by a neat ruse.
'Where is the autogyro?' Doc asked.
'Why, this Clark Savage who telephoned the plane had been stolen asked us to send a man with it to bring him here and confront the thief!'
Monk let out a loud snort. 'You dumb dude! You're talkin' to Clark Savage!'
The attendant stuttered again. 'I don't understand — '
'Some one foxed you,' Doc said without noticeable malice. 'The pilot who flew that plane to get the fake Clark Savage may be in danger. Do you know where he went?'
'The manager knows.'
They hurried over to the administration building. They found a Ham who was burning up. Ham could ordinarily talk himself out of almost any situation, given a little time. But he hadn't made an impression on the blond, bulletheaded airport manager.
Doc handed Ham a phone. 'Get the nearest army flying field, Ham. See if you can raise me a pursuit ship fitted with machine guns. It's against regulations, but — '
'Hang regulations!' Ham snapped, and seized the instrument.
From the blond airport manager Doc learned where the autogyro had gone to meet the man who had put over the trick. The spot was in New Jersey.
Doc located it on the map. It was in the mountainous, or, rather, hilly, western portion of Jersey.
Ham cracked the telephone receiver onto its hook. 'They're warming up a pursuit job for you, Doc.'
It required less than ten minutes for Doc to ferry over to the army drome, plug his powerful frame into a cockpit, saw the throttle back, and take off. He had a regulation war plane now.
Flying northward, Doc had a fair idea of the purpose of their enemy in decoying the autogyro. The place was within motor distance of New York, so the villainous unknown one would probably be on hand. He would destroy the autogyro, thus hampering Doc and his friends all possible.
'Whoever it is, they're willing to do anything to keep us from getting to that legacy of mine in Hidalgo!' Doc concluded.
Over the Delaware River, Doc dived and tested his machine guns by shooting at the shadow of his plane on the water.
Knobby green hills sprang up underneath. Doc used a pair of binoculars to scrutinize the terrain.
Farmhouses were scattering, ramshackle. Very few of the roads were paved.
Doc discovered his autogyro at last.
The windmill plane sat in a clearing. Near by ran a paved road.
In the clearing with the plane was a green coupe and two men. One of the men was holding a gun upon the other.
The gun wielder, Doc perceived when he came nearer, was masked. The man discovered Doc's army pursuit plane, diving with motor cans a-thunder. The fellow took fright.
Deserting the other man, who must be the autogyro pilot, the masked fellow raced to the windmill plane. The gun in his fist spat a bullet into the fuel tank of the plane. Gasoline ran out in two pale strings. The masked man struck a match and tossed it into the fuel. Instantly the autogyro was bundled in hot flame.
One thing Doc noted about the masked man — the fellow's fingers were a deep scarlet hue for an inch of their length!
The man was also squat and wide. He ran with shortlegged, pegging steps for the green coupe, dived into it. The green car ran out of the field like a frightened bug.
Doc's cowl machine guns released a spray of lead that forked up dust behind the coupe. The car skewered onto the road and turned north.
Again Doc's Browning guns tore off their ripping cackle of death. After the army fashion, every fifth bullet in the ammo cans was a phosphorous-filled tracer. These burst with hot red blots directly behind the green coupe.
Slowly, inexorably, the gray cobwebs of tracer smoke climbed into the rear of the automobile.
With a wild swing, the green car suddenly left the pavement. It vaulted a ditch, miraculously remaining upright, and skewered to a stop amid tall bush that practically hid it.
Doc distinctly saw the passenger quit the car and take to the concealment of the timber.
A couple of times Doc dived and let the Browning guns spew their twelve hundred shots a minute into the timber. He did it more to give the masked man one last scare than from any hope of bagging the fellow. The timber offered perfect concealment.
Not a little disgusted, Doc landed and launched a hunt afoot for the masked man. But it was too late.
The airport attendant who had flown the autogyro here could give no worthwhile description of the masked man when Doc consulted him. The fellow had merely sprung out of the green car with a gun.
Doc telephoned the authorities and had a net spread for the masked man before he took off again for Washington. But he was pretty certain the fellow would evade the Jersey officers. The man was smart, as well as
