belt.

The boy could run, but at thought of that he seemed to feel a twinge of pain from a knife in his back.

As he stood there, nerves all aquiver, oddly enough he thought of the mysterious eye blinking out of the wall back there in the hall. He wondered vaguely what it all meant and how this affair was to end.

And then quite suddenly the affair of the moment ended. The tall man uttered a low grumble which Johnny did not understand. Next instant the pair faded into the darkness, leaving him free to go his way in peace.

“Strange business, all of this,” he murmured to himself. He felt for the roll of bills that had been paid him for the professor’s library. Yes, they were still there.

“He said, ‘Come back tomorrow.’ The professor said that,” he mumbled as he hurried away. “Said I would meet dangers. W-e-l-l—”

He walked three blocks in deep thought. The whole business had thus far been very strange. What of the future?

How little he knew! Tomorrow lay before him, and after that tomorrow and another tomorrow. The task he had agreed to undertake was strange beyond belief.

Yet, for the most part ignorant of all this, he slept well that night and appeared next morning, suitcase in hand, ready for work at the door of that mystery house. In the broad light of day the place had lost much of its air of mystery.

He was relieved to find Felix Van Loon sitting on the doorstep waiting for him.

“Won’t have to run the gauntlet of eyes in the wall and submit my skeleton for inspection this time,” he whispered to himself.

“Come on in and have a cup of coffee with me before we get down to work,” the other boy welcomed.

“Be glad to,” Johnny answered.

“Watch!” Felix said a moment later. He pressed a button, then shot a wooden panel to one side, revealing a recess.

In that dark hole in the wall things began to happen. Two electric coils began to light up. At the same time Johnny noted with a start that two red eyes were gleaming from the darkest corner.

“Eyes,” Felix murmured. “They’ll do your work if you let them.”

Felix made no further comment. Johnny did not feel free to ask questions about the riddle of the “Eye.”

Dropping into a chair, Felix stared for a full two minutes at a crack in the floor. Then with a start he sprang to his feet, threw open a second panel and proceeded to draw forth a steaming pot of coffee and a plate of toast. Johnny recalled the professor’s remarks regarding the “Eye” but said nothing.

“It’s a queer place,” he told himself.

As if reading his thoughts, Felix put down his cup. “Father’s what they call an electrical wizard,” he said. “He does things no one dreams of. Enjoys it a lot, he does. So do I. But Father has a deep purpose in it all, thinks electricity may help to save the race; anyway that’s what he calls it.”

Once more he lapsed into silence. Johnny searched the dark corners of the room for peering eyes, but could find none.

“Through?” Felix asked quite suddenly. “All right then, let’s be on our way.” He strode across the room to catch up a kit of tools.

A moment more and they were in the street marching south. They had passed one brownstone building and were approaching a second when Felix drew Johnny into a doorway.

“Ought to tell you, I guess.” His voice was low. “Sort of warn you in case anything happens. Bit irregular, the thing we are about to do. If it frightens you after I’ve told you, just say so. Every fellow has a right!

“You see,” he got a fresh start, “Father was once in the secret service. He became interested at that time in working out devices for trapping criminals. And they should be trapped.” His voice rose. “Ninety per cent of all crimes are committed by men who never work. Professional criminals, they make life unsafe for everyone. But Father doesn’t trap ’em. He just works out the traps. He’s too much interested in making things to think much about using them himself. See that brick place, second door over?” His voice dropped. “Some queer ones live there—a tall one and a short one.”

“Tall one and a short—! I—”

“Not much time.” Felix held up a hand. “Sleep late, those two, but not too late. Got to get in and do some things before they come downstairs.

“We’re supposed to be changing some electric light switch boxes, you and I. That is, if we’re caught. You’re my helper. No breaking in or anything like that. Got the key from the owner. But if they come down, that tall one and the short one, they might get a little rough. See? Question is, are you still with me?” he concluded.

“Hundred per cent!” There was no hesitation in Johnny’s tone. For all that, there was a sense of dizziness in his head. He was seeing again the living skeletons, one with a knife on its hip, the other with a blade hanging from its bony fingers.

“All right,” said Felix, “let’s go!”

“But why should we change the switch boxes in that place?” Johnny asked.

“Rule one of our clan is, ‘No questions asked’!” Felix chuckled.

A moment more and a key turned in a lock. They found themselves in an ancient parlor. The place was dark and silent, reeking with mystery.

“Here you are.” Felix handed Johnny a large flashlight. “Just focus that on my hands while I work. Won’t try to raise the shades. Might disturb our friends upstairs. Might—Sh! Listen!” The red-haired boy backed against the wall.

Involuntarily Johnny gripped the handle of a hammer with his free hand. The memory of a knife blade protruding from a sleeve was fresh in his mind.

For a space of seconds the two boys remained motionless.

“Thought I heard something.” Felix moved forward. A moment more and his long capable fingers, trembling slightly, were busy removing an electric punch button from the wall.

“Good!” he whispered. “Hole’s large enough.”

Diving into his kit, he brought out a small metal box wrapped about with wires.

After unwinding these wires, he stood again at attention. Catching no sound, he resumed his work. Pushing the wires through the hole left by the removal of the punch button, he slid them down between the walls, then prepared to fit the black box into position.

“Perfect,” he sighed. “Couldn’t have been better! I—”

He held up a finger for silence. There had come a faint sound from above.

“Like a bare foot touching the floor,” Johnny thought. Once more he gripped his hammer handle hard. If they were attacked he would do his bit. But would that be enough? Strange business this! A chill crept up his spine.

Felix resumed his work. His fingers flew. “There!” he sighed. “They’d never know a thing has been changed. And yet—”

A moment later he disappeared into the depths of a large closet. What he did there Johnny was not permitted to know. For a full quarter of an hour, alternately chilling and thrilling at every sound that reached his ears, Johnny stood there on guard.

“Now,” the other boy at last whispered in his ear, “we go this way.” They passed through a door and down a stair into a cellar dark as night.

“One minute here, and then for the outer air.” Felix moved forward cautiously. For all that, his foot struck some object that gave forth a low, hollow roar. At the same instant there came from above an unmistakable sound of