Something about the lonely figure of the girl caused Edward Vail to bring his car to a sudden stop at the side of the road. When first he had glimpsed her off there on that narrow strip of rock-bound coast he was mildly surprised, for it was a desolate spot and seldom frequented by bathers so late in the season. Now he was aroused to startled attention by the unnatural posture of the slender body that had just been erect and outlined sharply against the graying September sky. He switched off the ignition and sprang to the ground.

Bent backward and twisted into the attitude of a contortionist, the little figure in the crimson bathing suit was a thing at which to marvel. No human being could maintain that position without falling, yet the girl did not fall to the jagged stones that lay beneath her. She was rigid, straining. Then suddenly her arm waved wildly and she screamed, a wild gasping cry that died in her throat on a note of despairing terror. It seemed that she struggled furiously with an unseen power for one horrible instant. Then the tortured body lurched violently and collapsed in a pitiful quivering heap among the stones.

Eddie Vail was running now, miraculously picking his way over the treacherous footing. The girl had fainted, no doubt of that, and something was seriously wrong with her.

A mysterious mechanical something whizzed past; something that buzzed like a thousand hornets and slithered over the rocks in a series of metallic clanks. Then it was gone--or so it seemed in the confusion of Eddie’s mind; but he had seen nothing. Probably a fantasy of his overworked brain, or only the surf breaking against the sea wall. He turned his attention to the girl.

She was moaning and tossing her head, returning painfully to consciousness. He straightened her limbs and placed his folded coat under the restless head, noting with alarm that vicious red welts marred the whiteness of her arms and shoulders. It was as if she had been beaten cruelly; those marks could never have resulted from her fall. Poor kid. Subject to fits of some sort, he presumed. She was a good looker, too, and no mistake. He smoothed back the rumpled mass of golden hair and studied her features. They were vaguely familiar.

Then she opened her eyes. Stark terror looked out from their ultra-marine depths, and her lips quivered as if she were about to cry. He raised her to a more comfortable position and supported her with an encircling arm. She did cry a little, like a frightened child. Then, with startling abruptness, she sprang to her feet.

“Where is it?” she demanded.

“Where’s what?” Eddie was on his feet, peering in all directions. He remembered the queer sounds he had heard or imagined.

“I--I don’t know.” The girl passed a trembling hand before her eyes as if to wipe away some horrifying vision. “Perhaps it’s my imagination, but I felt--it was just as real--one of father’s iron monsters. Beating me; bending me. I’d have snapped in a moment. But nothing was there. I--I’m afraid...”

Eddie caught her as she swayed on her feet. “There now,” he said soothingly, “you’re all right, Miss Shelton. It’s gone now, whatever it was.” Iron monsters! In a flash it had come to him that this girl he held in his arms was Lina Shelton, daughter of the robot wizard. No wonder she was afflicted with hallucinations! But those bruises were real, as was the forcible twisting of her lithe young body. And he had heard something.

“You know me?” The girl was calmer now and faced him with a surprised look.

“Yes, Miss Shelton. At least I recognize you from the pictures. Society page, you know. And I’m Edward Vail--Eddie for short--on vacation and at your service.”

The girl smiled wanly. “You know of father’s break with Universal Electric? Of his private experiments?”

“I heard of the scrap and of how he walked out on the outfit, but nothing further.” Eddie thought grimly of how nearly he had come to losing his own job when David Shelton broke relations with his employers. He had been too enthusiastic in support of some of the older man’s claims.

“It’s been terrible,” the girl whispered. She clung nervously to his arm as he picked the way back to the road. “The loneliness, and all. No servants will stay out here now, and father spends all of his time in the laboratory. Then--this fear of the mechanical men--they haunt me. I--I guess they’ve got me a little goofy.”

Eddie laughed reassuringly. “Perhaps,” he suggested, “you will let me help you. Your father, I believe, will remember me, and I’ll be very glad to--”

“No, no!” The girl seemed frightened at the thought. “I’m sure he wouldn’t welcome you. He’s changed greatly of late and is suspicious of everyone, even keeping things from me. But it’s awfully nice of you to offer your assistance, and you’ve been a perfect peach to take care of me this way. I--I’d better go now.”

They had reached the road and Eddie looked uncertainly at his roadster. He hated to think of leaving the girl in this lonely spot. She was obviously in a state of extreme nervous tension and, to him, seemed pathetically helpless, and afraid.

“That the house?” he asked, pointing in the direction of the gloomy old mansion whose dilapidated gables were barely visible over the tree tops.

“Yes.” The girl shivered and drew closer to him.

The ensuing silence was broken by the slam of a door. His car! Eddie looked toward it in amazement; he was hearing things again. The springs sagged on the driver’s side as under the weight of a very heavy occupant, but the seat was empty. Then came the whine of the starter and the motor purred into life. The gears clashed sickeningly and the car was jerked into the road with a violence that should have stripped the differential. He pulled the girl aside just as it roared past and disappeared around the bend in a cloud of dust. The sound of the exhaust died away rapidly and left them staring into each other’s eyes in awed silence.

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 passing 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 knob, and one of those buzzing, unseen, monstrosities rushed clanking by, knocking the scientist from his feet in its passage. 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 God! 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.”

Eddie was examining the intricate apparatus. “You knew of the first one’s escape, didn’t you?” he asked. “How did it happen?”

Shelton again became the enthusiastic scientist. “Here,” he said, “I’ll show you and you can judge for yourself.” He strode to the gleaming figure of a seven-foot robot of startlingly human-like appearance.

Lina let forth an exclamation of repugnance and fear.

“No, Mr. Shelton,” Eddie objected. “The same thing will occur again. Then there will be three.”

“We’ll fix that, my boy.” The scientist was removing cover plates from the hip joints of the mechanical man. “I’ll disconnect the cables that feed the locomotors. He can’t walk then.”

Eddie was still doubtful but dared offer no further objection, especially since Lina Shelton was watching in wide-eyed silence. He examined the monster and saw that it was quite similar in outside appearance to those supplied by Universal for heavy manual labor, excepting that this one was armed as were those used for prison guards. There were the same articulated limbs and the various clamps and hooks for lifting and heavy hauling; the tentacles for grasping; machine guns front and back. Under the helical headpiece that was the antenna this robot seemed to have two eyes--a new feature--but closer examination showed these to be the twin lenses of a stereoscopic motion picture camera. This robot, then, could see. Or at least it could record what the lenses saw for its masters.

“There,” Shelton grunted when he had finished his tinkering, “he’s paralyzed from the waist down. Let this one try and get away from us.”

“Guns aren’t loaded, are they?” Eddie asked.

“Lord, no! Never have any of them loaded. That would be a fool stunt.” Shelton had pulled the starting handle of a motor-generator and its rising whine accompanied his words.

The vacuum tubes of the transmitter glowed into life and the scientist manipulated the controls rapidly. Lina was watching the robot with fascinated awe. Its arms moved in obedience to the controls, tentacles waved and coiled; the humming of its internal mechanisms filled the room. The locomotion controls had no effect, as the scientist had predicted. Eddie drew a sigh of relief.

“Now, Vail, watch,” Shelton exulted. “I’ll show you what I was doing with the first one.” He closed a switch that lighted another bank of vacuum tubes behind the control panel.

“You can make this one invisible?” Eddie asked incredulously.

“Certainly--from the waist up. This ought to be good.”

“Mind telling me the principle?”

“Not at all--now. I’ve your promise of secrecy. It’s a simple matter, Vail, really. Just a problem of wave motions--light. Invisible light; the ultra-violet, you know. My robots are built of specially alloyed metals which permit great freedom of molecular vibration. The insulating materials and even the glass of the camera lenses are possessed of the same property. Get it? I merely set up a wave motion in the atoms of the material that is in synchronism with the frequency of ultra-violet light, which is invisible to the human eye. All visible colors are absorbed, or more accurately, none are reflected excepting the ultra-violet. Perfect transparency is obtained since there is neither refraction nor diffraction of the visible colors. And there you are!”

Eddie stared at the upper half of the robot and saw that it was changing color as Shelton tuned the transmitted wave. Then suddenly it was gone. The entire upper portion of the mechanism had vanished; had just snuffed out like the flame of a candle. He could see down into the tops of the thing’s hollow legs. Shelton laughed at him as he stretched forth his hand and hesitatingly felt for the invisible mid-section and upper body. It was there all right, unyielding and cold, that metal body. But no trace of it was visible to the eye. He drew back his fingers as if they had touched a hot stove. The thing was positively uncanny.

“Dad! Turn it off--please,” Lina begged. “It’s getting on my nerves. Please!”

Obligingly, Shelton pulled the switch. “Now you’ll see,” he said to Eddie, “whether the same thing happens. Watch.”

Mistily at first, the outlines of the monster’s torso and arms came into view, semi-transparent but clouding rapidly to opacity. Then it glinted with the barely visible violet, a solid once more, rigid and motionless. It was a lifeless mechanism, for the source of its energy had been cut off. Eddie had an almost irresistible impulse to pinch himself.

Then he gasped audibly, as did Shelton, for the thing snuffed out of sight again without warning, and the hum of its many motors resumed. There came a terrific clanking as it waved arms and tentacles and violently threshed with its upper body. But the visible portion, its legs, remained rooted to the floor of the laboratory. Lucky it was that the scientist had disconnected those wires; lucky too that the machine guns were empty of ammunition.

“There now--see?” Shelton’s voice rose excitedly. “It’s been no fault of mine. The power is off but it moves--it moves. What on earth do you suppose--”

Eddie’s shout interrupted him. He had seen something at the window: a face pressed against the pane and contorted with unutterable malice. Then it was gone. With the shout of warning still in his throat, Eddie bounded through the door in pursuit of the intruder. Lina’s cry of recognition followed him into the twilight. “Carlos!” she had called.

He saw a stocky figure slink around the corner of the laboratory and make for the underbrush beyond. In a flash he was after him. No, he thought grimly, Shelton hadn’t any enemy clever enough to duplicate his transmitter! The hell he didn’t! Who the devil was this fellow Carlos anyway? He tore savagely at the impeding branches as he plunged deeper and deeper into the thicket.

It was a fruitless chase and Eddie soon retraced his steps to the laboratory. Swell mess he’d gotten himself into! His car was gone: probably wrapped around a tree by this time. And here was a situation that spelled real danger, a thing with which Shelton was utterly unable to cope. As a matter of fact, he was so impractical--such a visionary cuss, after the fashion of all geniuses--that he’d never be convinced of the seriousness of the matter until it was too late. What to do? The girl was a corker, though, and game as they made ‘em. Just the sort a fellow could tie to...

Lina’s firm clear voice came to him through the open door of the laboratory. “Dad,” she was saying, “why don’t you give it up? Let’s go back to New York where it is safe for you and for me. Let the things go and forget about them. What do they amount to, after all? We’ve plenty of money and you already have earned enough fame to last the rest of your life. Come on now--please--for me.”

“What do they amount to?” Shelton reiterated, his voice rising querulously. “Lina, it’s the most tremendous thing I’ve ever done. Think for a moment of what my robots could accomplish in the next war. And there’ll be a next war as sure as you’re alive. Think of it! No sending of our young manhood into the bloody fields of battle; no manning of our air fleets with the cream of our youth; no bloodshed on our side whatsoever. Instead, these robots will fight the war. They’ll fight other robots too, no doubt, but the property of invisibility will be an invincible weapon. It will be a war that will end war once and for all. You can’t--”

“Nonsense, Father,” the girl returned sharply. “You’ve let your enthusiasm run away with your judgment. See what’s happened already?--someone’s figured it out before you’ve even perfected the thing. An enemy of our country could do the same in wartime. Maybe it’s a foreign spy who has done what’s been done to-day.”

Eddie walked into the laboratory. “Couldn’t find him,” he announced briefly.

“No difference,” said Shelton. “He doesn’t count in this. We called to you when you rushed out, but couldn’t make you hear.”

“Who is he?” Eddie asked shortly. What he had overheard made him more than ever impatient with the older man. So clever and yet so dense, Shelton was.

Lina avoided his gaze.

“Only Carlos--Carlos Savarino,” said Shelton, carelessly, “a Chilean, I think. He worked for me for two months during the summer and I fired him for getting fresh with Lina. Good mechanic, but dumb as an ox. Had to tell him every little detail when he was doing something in the shop. I’d have saved time if I’d done it myself.”

The girl looked at Eddie squarely now. She was flushing hotly. “And I horsewhipped him,” she added.

“Yes,” Shelton laughed; “it was rich. He sneaked away like a whipped puppy, and this is the first time we’ve seen him since.”

Eddie whistled. “And you think he doesn’t count in this?” he asked.

“Of course not. Too dumb, I tell you. Doesn’t know the first principles of science. He thinks the only wave motion is that of the ocean.” Shelton chuckled over his own jest.

“I wouldn’t be too sure,” Eddie snapped. “And I want to tell you something, Mr. Shelton. Through no fault of my own, I heard some of your conversation with Li--with your daughter, before I returned here. I was puzzled over your reasons for working so absorbedly on this thing, but now I know them and I think you’re wasting your time and keeping your daughter in needless danger.”

“You dare talk to me like this!” Shelton roared.

“I do, sir, and you’ll thank me later.” Eddie returned the older man’s glare with one equally savage.

Lina’s gurgle of laughter broke the tension. “He’s right, Dad, and you know it,” she interposed. “Let him finish.”

Eddie needed no such encouragement, though it warmed his heart. And Shelton listened respectfully when he continued, “I’m into this now, sir, and I intend to see it through to the end. I’ll keep your secret, too, though I doubt if it’ll ever be of much value to you. Know what I think? I think this Carlos is a damn clever fellow instead of the ass you took him to be. He probably just pretended he was ignorant of science. Why shouldn’t he? That way he got a liberal education from you in the very things he wanted to find out. Since you tied the can to him he’s had plenty of chances to build a duplicate of your control apparatus--with the aid of some foreign government, no doubt--and now they’ve stolen two of your machines to complete the job. Your secret already is out and in the very hands you’ve tried to keep it from.”

Shelton paled visibly as Eddie talked. “But--but how--” he stammered.

“How should I know how they did it?” the younger man countered. “Here--let’s take a look around. I’ll bet they’ve left their trail right here in this room.”

He walked from one end of the laboratory to the other, peering into corners and under work benches as he passed. Shelton trailed him like a shadow, squinting through the square lenses of his spectacles.

They carefully avoided the partially invisible robot, for the humming of its upper motors continued and clanking sounds occasionally issued from the unseen upper portion. The enemies of David Shelton were still at work on their hidden controls.

“Here--what’s this?” Eddie exclaimed suddenly, pointing out a glinting object in a dark corner of the laboratory.

Shelton examined it closely, looking over his shoulder. The object he had located seemed to be a mounted and hooded lens, a highly polished glass of about two inches diameter with its mounting attached rigidly to the wall.

“Never saw that before,” Shelton stated with conviction. “And--why--it looks like an objective such as those used in the latest automatic television transmitters.”

“Just what it is,” Eddie grunted. He picked up a pinch bar from a nearby tool rack and drove its end through the glass as he spoke the words.

A violent wrench tore the thing loose and broke away a section of the thin plastered wall. There, in the cleverly concealed cavity behind, was revealed the mechanism of the radio “eye.” Somewhere, someone bad been watching their every move. And abruptly the thrashings of the robot ceased and its upper portion again became visible.

“Well,” said David Shelton. “Well! Looks as if you’re right, young man. I’m astonished.” His watery eyes looked sheepishly over the rims of his glasses.

Lina watched their every move. She seemed to sense the seriousness of the situation far more than did her father.

Then the lights went out. It had darkened to night outside and the blackness and silence in the laboratory was like that of a tomb.

“They’ve cut the wires,” Eddie whispered hoarsely. “Got any weapons here, Shelton?”

“Yes. A couple of automatics. I’ll get them.” The scientist was no coward, anyway. His whispered words came calmly through the silence.

Eddie heard him shuffle a few steps and fumble with a drawer of the desk. In a moment the cold hard butt of a pistol was thrust into his hand. It had a comforting feel.

“Stay here with Lina,” he commanded. “I’ll go out and see if I can find them. This looks nasty to me.”

“No,” came the girl’s voice, “I’m going too.”

“You are not,” Eddie hissed. “You’ll stay here or I’ll know the reason. It’s dark as a pocket outside and my eyes are as good as theirs. I’ll get ‘em if they’re around here. You hear me?”

“Yes,” she whispered meekly.

Edward Vail, only that morning headed for rest and quiet, was now out in the night, stalking an unknown and vicious enemy. And--for what? As he asked himself the question, the smile of Lina seemed to answer him from the blackness. Cherchez la femme! He was getting dotty as he neared his thirties. Maybe it was the hard work that had affected his mind.

The black hulk of the old house loomed against the scarcely less dark sky. There was no moon, and in only one tiny portion of the heavens were the stars visible. Mighty few of them at that. The swish-swish of the surf came to his ears faintly. Or was it someone creeping along the wall of the house? He held his breath and waited.

They wouldn’t use the robots at night. Couldn’t follow their movements in the teleview, if such an attachment had been built into their control transmitter. No, the devils would be here in person.

A muttered Teutonic curse sounded close at hand. That wouldn’t be Carlos. God! Were the heinies mixed up in this thing? Just like ‘em to be swiping a new war machine; but hadn’t they gotten enough in 1944? Without warning he was catapulted from his feet by the impact of a heavy body. He struck the ground so violently that the pistol was jarred from his hand. Disarmed before the fight had started!

Then he was rolling over and over, battling desperately with an assailant who was much larger and heavier than himself. He was dazed and weakened from his initial dive to the hard ground. All rules of boxing and wrestling were forgotten. Biting, kicking, gouging, all were the same to this silent and powerful antagonist. It was catch-as-catch-can in the darkness, and mostly the other fellow could and did. He had a grip like the clamp of a robot. Trying to dig out one of his eyes? Eddie saw stars--and lashed out with all his might, his flying fists playing a tattoo on the others ribs. Short arm jabs that brought grunts of agony from his big assailant. Try to blind him, would he?

Eddie somehow managed to get on top; his clutching fingers found the other’s collar. Then he let loose with terrific rights and lefts that smacked home to head and face. Those outlanders don’t like the good old American fist, and Eddie had room to bring them in from way back, now. The fellow had ceased struggling and Eddie’s hands were getting slippery. Blood! Must be, for the stuff was warm and sticky. He rested for a moment, breathing heavily. The other was quiet beneath him--knocked cold. He staggered to his feet triumphantly; wondered how many more of them there were.