Kennedy bent over his detector.

"That same mysterious buzzing," he muttered, "only fainter."

Together we hastened now toward the distillery, another of those corrugated-iron buildings. It had been completely demolished. Here and there lay a dark, still ma.s.s. I shuddered. They were men!

As we ran toward the ruin we crossed a baseball-field which the company had given the men. I looked back for Kennedy. He had paused at the wire backstop behind the catcher. Something caught in the wires interested him. By the time I reached him he had secured it--a long, slender metal tube, cleverly weighted so as to fall straight.

"Not a hundred per cent. of hits, evidently," he muttered. "Still, one was enough."

"What is it?" asked MacLeod.

"An incendiary pastille. On contact, the nose burns away anything it hits, goes right through corrugated iron. It carries a charge of thermit ignited by this piece of magnesium ribbon. You know what thermit will penetrate with its thousands of degrees of heat. Only the nose of this went through the netting and never touched a thing. This didn't explode anything, but another one did. Thousands of gallons of alcohol did the rest."

Kennedy had picked up his other package as we ran, and was now busily unwrapping it. I looked about at the crowd that had collected, and saw that there was nothing we could do to help. Once I caught sight of Gertrude's face. She was pale, and seemed eagerly searching for some one. Then, in the crowd, I lost her. I turned to MacLeod. He was plainly overwhelmed. Kennedy was grimly silent and at work on something he had jammed into the ground.

"Stand back!" he cautioned, as he touched a match to the thing. With a m.u.f.fled explosion, something whizzed and shrieked up into the air like a sky-rocket.

Far above, I could now see a thing open out like a parachute, while below it trailed something that might have been the stick of the rocket. Eagerly Kennedy followed the parachute as the wind wafted it along and it sank slowly to the earth. When, at last, he recovered it I saw that between the parachute and the stick was fastened a small, peculiar camera.

"A Scheimpflug multiple camera," he explained as he seized it almost ravenously. "Is there a place in town where I can get the films in this developed quickly?"

MacLeod, himself excited now, hurried us from the scene of the explosion to a local drug-store, which combined most of the functions of a general store, even being able to improvise a dark-room in which Kennedy could work.

It was some time after the excitement over the explosion had quieted down that MacLeod and I, standing impatiently before the drug-store, saw Snedden wildly tearing down the street in his car. He saw us and pulled up at the curb with a jerk.

"Where's Gertrude?" he shouted, wildly. "Has any one seen my daughter?"

Breathlessly he explained that he had been out, had returned to find his house deserted, Gertrude gone, his wife gone, even Jackson's car gone from the barn. He had been to the works. Neither Garretson nor Jackson had been seen since the excitement of the explosion, they told him. Garretson's racer was gone, too. There seemed to have been a sort of family explosion, also.

Kennedy had heard the loud talking and had left his work to the druggist to carry on and joined us. There was no concealment now of our connection with MacLeod, for it was to him that every one in town came when in trouble.

In almost no time, so accurately did he keep his fingers on the fevered pulse of Nitropolis, MacLeod had found out that Gertrude had been seen driving away from the company's grounds with some one in Garretson's car, probably Garretson himself. Jackson had been seen hurrying down the street. Some one else had seen Ida Snedden in Jackson's car, alone.

Meanwhile, over the wire, MacLeod had sent out descriptions of the four people and the two cars, in the hope of intercepting them before they could be plunged into the obscurity of any near-by city. Not content with that, MacLeod and Kennedy started out in the former's car, while I climbed in with Snedden, and we began a systematic search of the roads out of Nitropolis.

As we sped along, I could not help feeling, though I said nothing, that, somehow, the strange disappearances must have something to do with the mysterious phantom destroyer. I did not tell even Snedden about the little that Kennedy had discovered, for I had learned that it was best to let Craig himself tell, at his own time and in his own way.

But the man seemed frantic in his search, and I could not help the impression that there was something, perhaps only a suspicion, that he knew which might shed some light.

We were coming down the river, or, rather, the bay, after a fruitless search of unfrequented roads and were approaching the deserted Old Grove Amus.e.m.e.nt Park, to which excursions used, years ago, to come in boats. No one could make it pay, and it was closed and going to ruin.

There had been some hint that Garretson's racer might have disappeared down this unfrequented river road.

As we came to a turn in the road, we could see Kennedy and MacLeod in their car, coming up. Instead of keeping on, however, they turned into the grove, Kennedy leaning far over the running-board as MacLeod drove slowly, following his directions, as though Craig were tracing something.

With a hurried exclamation of surprise, Snedden gave our car the gas and shot ahead, swinging around after them. They were headed, following some kind of tire-tracks, toward an old merry-go-round that was dismantled and all boarded up. They heard us coming and stopped.

"Has any one told you that Garretson's car went down the river road, too?" called Snedden, anxiously.

"No; but some one thought he saw Jackson's car come down here," called back MacLeod.

"Jackson's?" exclaimed Snedden.

"Maybe both are right," I ventured, as we came closer. "What made you turn in here?'"

"Kennedy thought he saw fresh tire-tracks running into the grove."

We were all out of our cars by this time, and examining the soft roadway with Craig. It was evident to any one that a car had been run in, and not so very long ago, in the direction of the merry-go-round.

We followed the tracks on foot, bending about the huge circle of a building until we came to the side away from the road. The tracks seemed to run right in under the boards.

Kennedy approached and touched the boards. They were loose. Some one had evidently been there, had taken them down, and put them up. In fact, by the marks on them, it seemed as though he had made a practice of doing so.

MacLeod and Kennedy unhooked the boarding, while Snedden looked on in a sort of daze. They had taken down only two or three sections, which indicated that that whole side might similarly be removed, when I heard a low, startled exclamation from Snedden.

We peered in. There, in the half-light of the gloomy interior, we could see a car. Before we knew it Snedden had darted past us. An instant later I distinguished what his more sensitive eye had seen--a woman, all alone in the car, motionless.

"Ida!" he cried.

There was no answer.

"She--she's dead!" he shouted.

It was only too true. There was Ida Snedden, seated in Jackson's car in the old deserted building, all shut up--dead.

Yet her face was as pink as if she were alive and the blood had been whipped into her cheeks by a walk in the cold wind.

We looked at one another, at a loss. How did she get there--and why?

She must have come there voluntarily. No one had seen any one else with her in the car.

Snedden was now almost beside himself.

"Misfortunes never come singly," he wailed. "My daughter Gertrude gone--now my wife dead. Confound that young fellow Garretson--and Jackson, too! Where are they? Why have they fled? The scoundrels--they have stolen my whole family. Oh, what shall I do? what shall I do?"

Trying to quiet Snedden, at the same time we began to look about the building. On one side was a small stove, in which were still the dying coals of a fire. Near by were a work-bench, some tools, pieces of wire, and other material. Scattered about were pieces of material that looked like celluloid. Some one evidently used the place as a secret workshop.

Kennedy picked up a piece of the celluloid-like stuff and carefully touched a match to it. It did not burn rapidly as celluloid does, and Craig seemed more than ever interested. MacLeod himself was no mean detective. Accustomed to action, he had an idea of what to do.

"Wait here!" he called back, dashing out. "I'm going to the nearest house up the road for help. I'll be back in a moment."

We heard him back and turn his car and shoot away. Meanwhile, Kennedy was looking over carefully Jackson's roadster. He tapped the gas-tank in the rear, then opened it. There was not a drop of gas in it. He lifted up the hood and looked inside at the motor. Whatever he saw there, he said nothing. Finally, by siphoning some gas from Snedden's tank and making some adjustments, he seemed to have the car in a condition again for it to run. He was just about to start it when MacLeod returned, carrying a canary-bird in a cage.

"I've telephoned to town," he announced. "Some one will be here soon now. Meanwhile, an idea occurred to me, and I borrowed this bird. Let me see whether the idea is any good."

Kennedy, by this time, had started the engine. MacLeod placed the bright little songster near the stove on the work-bench and began to watch it narrowly.

More than ever up in the air over the mystery, I could only watch Kennedy and MacLeod, each following his own lines.

It might, perhaps, have been ten minutes after MacLeod returned, and during that time he had never taken his eyes off the bird, when I began to feel a little drowsy. A word from MacLeod roused me.

"There's carbon monoxide in the air, Kennedy!" he exclaimed. "You know how this gas affects birds."