hoped the professor might be able to pay him the money and take the library.

“Cost hundreds of dollars in the first place, those books,” he murmured. “You’d think—”

Again he broke off to listen and stare. Strange noises, curious flashes of light, and then the door swung open. The golden-haired girl appeared. The door closed behind her.

“He—he’ll be here soon.” She seemed breathless. “He—he’s working at something, a—a sort of trap. Do you know,” she whispered, “this is a terrible neighborhood—truly frightful! That is why we live here.”

“Curious sort of reason,” the boy thought, but he said never a word, for at that instant the clock-like affair on the wall began buzzing loudly, the red light blinked six times in quick succession.

“Oh!” There was consternation in the girl’s voice.

Seizing the astonished boy by the arm, she dragged him to a corner of the room. There he found himself looking at what appeared to be a narrow strip of mirror.

Upon that mirror moving objects began to appear. Before his astonished eyes these spots arranged themselves into the form of two skeletons, one tall, one short. Dangling from the hip-bone of the tall skeleton was what appeared to be a long knife. Again the girl whispered, “Oh!”

But the short skeleton! Trembling so it appeared to dance, it slipped a knife along its bony wrist to at last grip it firmly in its skeleton fingers.

The girl touched a button here, another there. The thing on the wall buzzed. Words were spoken outside the door, indistinct words. The skeletons disappeared. There came the sound of a door closing.

“They—they’re gone!” The girl sighed.

Catching a slight sound of movement behind him, Jimmy whirled about to find himself looking into a pair of smiling blue eyes. “Here,” he thought to himself, “is the girl’s father, the professor.” There were the same features, the same shock of golden hair.

“I am Professor Van Loon,” the man said in a voice that was low, melodious and dreamy.

“Beth here tells me you bought my books,” he went on. “That was kind of you. We’ve been moving about a great deal. The books have followed us here and there. Charges piled up. Until quite recently money has been scarce. Then, I confess, I forgot. In these days one is likely to forget his choicest treasures.”

He turned to the girl. “Beth, who was at the door just now?”

“Two men.” She trembled slightly. “They carried knives, so I opened the door on the outside. They—they hurried away.”

“I dare say!” The professor chuckled dryly.

“Press the button, Beth,” the professor said, nodding his head toward the right wall. “Our guest will stay for cocoa and cakes, I am sure. That right?” he asked, turning to Johnny.

“I will, yes,” Johnny agreed.

The girl pressed a button like a lamp switch in the wall.

The boy’s feelings were mixed. He wanted to stay. These people interested him and there were a hundred mysteries to solve,—living skeletons, eyes blinking from the walls, self-opening doors, lights that gleamed and clocks that buzzed.

A fresh mystery was added when five minutes later the girl pressed a second button and a tray laden with cups, saucers, a plate of cakes and a pot of steaming cocoa appeared.

“The ‘Eye’ did it for us,” the professor explained in a matter-of-fact tone. “In these days one scarcely needs a servant even when he is able to afford one.”

Perhaps Johnny would have said, “What is the ‘Eye’?” but at that moment the door at the rear opened and a tall youth with tumbled red hair appeared.

The professor rose. “Son, meet Johnny Thompson. Now we are all here.”

When, two hours later, Johnny left this place of enchantment, his head was in a whirl.

“Just goes to show,” he chuckled to himself, “that when you do an unusual stunt anything may happen—just anything at all.”

Several things had happened in the last two hours. He had come to have a high regard for the professor and his family. He had received payment in full for the professor’s library and a ten dollar bill thrown in for good measure.

“Boy alive!” the professor had exclaimed when he hesitated to accept this extra ten. “If some shark that haunts those auctions had got my books it would have cost me a small fortune to redeem them.”

All this had happened, and much more.

“Best of all,” Johnny whispered to himself, “I am no longer alone. I’ve made a place for myself.” Just what sort of place it was, he did not surely know.

“I should like to have you cast in your lot with us,” the professor had said. “A boy who thinks of others, as you have done in this library affair, is sure to be of service anywhere.

“We do strange and interesting things here.” The professor’s eyes had twinkled. “Sometimes they are useful and practical; sometimes they are not. Always they are absorbing, at times quite too startling. At times we have money, at others none. Just now we are quite rich.” He chuckled. “Someone offered us a great deal of money for an electric contraption that sorts beans, sorts a car load a day. Who wants that many beans?” He chuckled again. “Anyway we have money and they can sort beans. Money means material, equipment for fresh experiments. You will come with us?” He squinted at Johnny.

“Yes. Yes, sure.” Johnny scarcely knew what leg he was standing on. “Queer business!” was his mental comment.

“We will exact only one promise,” the professor continued. “You’ll not pry into our secrets. Such secrets as we entrust to you you will divulge to no man. Do you promise?”

“I promise.”

“You’ll learn a lot and enjoy the work a heap,” the son had said to Johnny.

“I want you to know,” the professor had added in a sober tone, “that if you come with us you may be in some danger; in fact I’m quite certain that I can promise it, yet it will never be foolhardy nor reckless danger. You’ll come to live with us. That is necessary.”

“That’s O.K.,” Johnny had agreed.

And now Johnny found himself outside in the cool air of night, the lake breeze fanning his cheek, wondering if it all—the living skeletons, eyes blinking in the wall, the self-closing doors—all had been a dream.

“No!” He crushed the roll of bills in his pocket. “No, it was real enough. I—”

Suddenly two shadows materialized from a doorway, one tall, one short.

“The—the two men of the living skeletons, the ones that girl and I saw in the mirror!” he whispered, catching his breath sharply. If there had been any question in his mind regarding this last conclusion it was dispelled instantly. An inch of white steel, a knife blade, protruded from the short person’s sleeve as he muttered menacingly, “Stand where you are!”

CHAPTER II
SOMETHING RATHER TERRIBLE

Johnny Thompson was no weakling. He was a lightweight boxer. He had made his way over the frozen wastes of Alaska and through the jungles of Central America and many other wild places as well. This city held little terror for him.

As he faced the two strangers in the semi-darkness of the street, he considered tackling the little man.

“If I tackle low I’ll catch him off his guard, bowl him over like a tenpin. But the other, the tall one?” Ah, there was the rub! He carried a knife at his