David Shelton was prowling around in the shrubbery when they approached the house--a furtive, unkempt creature whom Eddie would hardly have recognized. He straightened up and peered at his daughter's companion with obvious disapproval.

"Lina," he said severely, "I've told you we want no visitors."

"Yes, Dad, I know, but Mr. Vail's car was stolen out in front and there is no way for him to go on. We must look after him."

"His car--stolen? Who stole it?" David Shelton drew close and glared suspiciously at his unwelcome visitor.

"One of your monsters, I think," she replied shakily, "though we could see nothing. And the same thing attacked me and beat me. Look at my bruises!"

Shelton was examining the marks, and his fingers trembled as he touched his daughter's shoulder. He looked piteously into her eyes.

"Are you sure, Lina? Sure? Did you see it?"

"No, no. But I felt and heard--the iron arms and the clamps and the buzzing. Oh, it was horrible!" The girl's voice rose hysterically.

"Oh, Lord! What have I done?" groaned Shelton. "It's true, then. Lina, listen: I've succeeded in making them invisible, and one got away this morning. But I thought--I thought--" He looked at Eddie, remembering his presence suddenly. "But I'm talking too much. It seems to me I remember having seen you before, young man."

"You have, sir," Eddie stated. "In the research laboratory of Universal Electric. I work with Borden."

"They've sent you to find me?" Shelton stiffened perceptibly.

"Indeed, not, sir. I'm on vacation and was merely pa.s.sing by when I saw your daughter in danger, a danger I still do not understand."

"Yes, and he helped me to the road," Lina interposed, "and then lost his car at the hands of--"

"Silence!" the father thundered. But his eyes fell before the fire that instantly flashed in those of the girl.

"Now, you listen to me!" she returned angrily, "I've stayed on here with you until I'm nearly crazy with your everlasting puttering and experimenting--hearing your uncanny machines walking around in the middle of the night--seeing impossible sights--then, this thing I couldn't see but could feel. And you've gotten into such a state that you'll go crazy yourself, if you continue. Something's got to be done, I tell you. I can't stand it!"

Her voice broke on a choked sob.

"But Lina--"

"Don't but me, Father. I mean it. Mr. Vail discovered your hideout quite by accident and he's been very nice to me. I tell you he means no harm and I want him to stay. If you're not decent to him, if you send him away, I swear I'll go too. I will--I will!"

Shelton's eyes misted and something of the hardness left his expression. A look of haunting fear took its place and he stared pleadingly at Eddie.

"Br-r! I'm cold!" Lina exclaimed irrelevantly. "And--and I believe I'm going to cry." She turned away and raced for the shelter of the gloomy old house without another word.

Eddie turned inquiring eyes on his unwilling host.

"Just like her mother before her," Shelton muttered softly. Then he faced the younger man squarely and his shoulders straightened. "Mr.

Vail," he said sheepishly, "I've been a fool and I ask your pardon.

But Lina doesn't know. There's something tremendous behind all this, something that's gotten beyond me. I'll send her away for her own safety, but I must stay on. If--if only there was someone I could trust--"

"You can trust me, sir," Eddie stated simply.

The older man paced the ground nervously, and Eddie could see that he was under a most severe mental strain. Several times he halted in his tracks and peered anxiously at his guest. Then he seemed to make a sudden decision.

"Vail," he said sharply, "I need help badly. I want you to stay, if you will. You swear you'll not reveal what I am about to show you?"

"I swear it, sir."

"You'll not report to Universal?"

"Never."

They surveyed each other appraisingly. Eddie was mystified by the happenings of the day and was curious to learn more concerning these mythical invisible creations. It was inconceivable that the scientist had spoken truly of his accomplishment. Yet, he had done some marvelous things with Universal and, maybe--well, anyway, there was the girl.

"Come with me," Shelton was saying: "I believe you're a square shooter, Vail." He was leading the way along the gravel path at the side of the house. Before them loomed the squat brick building that was the laboratory.

The door crashed open before Shelton's hand had reached the k.n.o.b, and one of those buzzing, unseen, monstrosities rushed clanking by, knocking the scientist from his feet in its pa.s.sage. Ponderous, speeding footsteps crunched the gravel of the path, and then, with a wild thrashing of the underbrush alongside, the thing was gone.

Eddie bent over the prostrate man and saw that he was unconscious. A thin trickle of blood ran from a cut in the side of his head.

"Lina! Lina!" called Eddie frantically. For the first time in his life he was genuinely frightened.

He half carried, half dragged the limp body through the door of the laboratory and propped it in a chair. It required but a moment for him to see that Shelton's injury was inconsequential. He had only been stunned and already showed signs of recovering.

"What is it, Mr. Vail? What's happened?" came the voice of Lina Shelton breathlessly. She was framed in the doorway, dressed now and panting from her exertions in responding to his call. "Oh, it's father," she wailed, dropping to her knees at his side. "He's been hurt. Badly, too."

"No, not badly, Miss Shelton. He'll be around in a minute. I'm sorry to have excited you, but when I called I feared it was worse than it is." He was washing the blood from her father's small wound as he spoke.

She took the basin from his hand, spilling some of the water in her eagerness. "Here, let me have that cloth," she demanded.

Eddie admired her as her deft fingers took up the task. She was as exquisite in a simple sport outfit as she had been in her bathing suit.

The scientist opened his eyes after a moment. Remembrance came at once and he sat erect in the chair, staring.

"Lina!" he exclaimed, grasping her hand conclusively. "You're here, thank G.o.d! I dreamed--oh, it was horrible--I dreamed they had you." He clung to her closely.

"They?" she murmured inquiringly.

"Yes. Two of them are loose now. It's danger for you, my dear. You must leave at once. No, no--I can't let you out of my sight until they are captured or destroyed." He rose to his feet in his agitation and shook his head to clear it. He looked pleadingly at Eddie as if expecting him to offer a solution of the difficulty.

"Vail!" he exploded, then, pointing a shaking forefinger at an elaborate short-wave radio transmitter which occupied a corner of the large room. "I ask you to bear witness. That is the source of energy for these creations of mine and it's shut down. How on earth can they keep going? I ask you."

"Perhaps someone else, sir," Eddie suggested doubtfully. "Have you any enemies who might be able to duplicate the impulses of that apparatus?"

"Bah! Enemies, yes--with Universal--but none who could duplicate the complicated frequencies I use. My secrets are my own. I've never even put them on paper."