From somewhere out on the black, heaving Atlantic, the rapid, muffled popping of a speed-boat’s exhaust drifted clearly through the night.

I dropped my book and stretched, leaning back more comfortably in my chair. There was real romance and adventure! Rum-runners, seeking out their hidden port with their cargo of contraband from Cuba. Heading fearlessly through the darkness, fighting the high seas, still running after the storm of a day or so before, daring a thousand dangers for the sake of the straw-packed bottles they carried. Sea-bronzed men, with hard, flat muscles and fearless eyes; ready guns slapping their thighs as they--

Absorbed in my mental picture of these modern free-booters, the sudden alarm of the telephone startled me like an unexpected shot fired beside my ear. Brushing the cigarette ashes from my smoking-jacket, I crossed the room and snatched up the receiver.

“Hello!” I snapped ungraciously into the mouthpiece. It was after eleven by the ship’s clock on the mantel, and if--

“Taylor?” The voice--Warren Mercer’s familiar voice--rattled on without waiting for a reply. “Get in your car and come down here as fast as possible. Come just as you are, and--”

“What’s the matter?” I managed to interrupt him. “Burglars?” I had never heard Mercer speak in that high-pitched, excited voice before; his usual speech was slow and thoughtful, almost didactic.

“Please, Taylor, don’t waste time questioning me. If it weren’t urgent, I wouldn’t be calling you, you know. Will you come?”

“You bet!” I said quickly, feeling rather a fool for ragging him when he was in such deadly earnest. “Have--”

The receiver snapped and crackled; Mercer had hung up the instant he had my assurance that I would come. Usually the very soul of courtesy and consideration, that act alone would have convinced me that there was an urgent need for my presence at The Monstrosity. That was Mercer’s own name for the impressive pile that was at once his residence and his laboratory.

I threw off the smoking-jacket and pulled on a woolen golfing sweater, for the wind was brisk and sharpish. In two minutes I was backing the car out of the garage; a moment later I was off the gravelled drive and tearing down the concrete with the accelerator all the way down, and the black wind shrieking around the windshield of my little roadster.

My own shack was out of the city limits--a little place I keep to live in when the urge to go fishing seizes me, which is generally about twice a year. Mercer picked the place up for me at a song.

The Monstrosity was some four miles further out from town, and off the highway perhaps a half-mile more.

I made the four miles in just a shade over that many minutes, and clamped on the brakes as I saw the entrance to the little drive that led toward the sea, and Mercer’s estate.

With gravel rattling on my fenders, I turned off the concrete and swept between the two massive, stuccoed pillars that guarded the drive. Both of them bore corroded bronze plates, “The Billows,” the name given The Monstrosity by the original owner, a newly-rich munitions manufacturer.

The structure itself loomed up before me in a few seconds, a rambling affair with square-shouldered balconies and a great deal of wrought-iron work, after the most flamboyant Spanish pattern. It was ablaze with light. Apparently every bulb in the place was burning.

Just a few yards beyond the surf boomed hollowly on the smooth, shady shore, littered now, I knew, by the pitiful spoils of the storm.

As I clamped on my brakes, a swift shadow passed two of the lower windows. Before I could leap from the car, the broad front door, with its rounded top and circular, grilled window, was flung wide, and Mercer came running to meet me.

He was wearing a bathrobe, hastily flung on over a damp bathing suit, his bare legs terminating in a pair of disreputable slippers.

“Fine, Taylor!” he greeted me. “I suppose you’re wondering what it’s all about. I don’t blame you. But come in, come in! Just wait till you see her!”

“Her?” I asked, startled. “You’re not in love, by any chance, and bringing me down here like this merely to back up your own opinion of them eyes and them lips, Mercer?”

He laughed excitedly.

“You’ll see, you’ll see! No, I’m not in love. And I want you to help, and not admire. There are only Carson and myself here, you know, and the job’s too big for the two of us.” He hurried me across the broad concrete porch and into the house. “Throw the cap anywhere and come on!”

Too much amazed to comment further, I followed my friend. This was a Warren Mercer I did not know. Usually his clean-cut, olive-tinted face was a polite mask that seldom showed even the slightest trace of emotion. His eyes, dark and large, smiled easily, and shone with interest, but his almost beautiful mouth, beneath the long slim mustache, always closely cropped, seldom smiled with his eyes.

But it was his present excited speech that amazed me most. Mercer, during all the years I had known him, had never been moved before to such tempestuous outbursts of enthusiasm. It was his habit to speak slowly and thoughtfully, in his low, musical voice; even in the midst of our hottest arguments, and we had had many of them, his voice had never lost its calm, unhurried gentleness.

To my surprise, instead of leading the way to the really comfortable, although rather gaudy living room, Mercer turned to the left, towards what had been the billiard room, and was now his laboratory.

The laboratory, brilliantly illuminated, was littered, as usual, with apparatus of every description. Along one wall were the retorts, scales, racks, hoods and elaborate set-ups, like the articulated glass and rubber bones of some weird prehistoric monster, that demonstrated Mercer’s taste for this branch of science. On the other side of the room a corresponding workbench was littered with a tangle of coils, transformers, meters, tools and instruments, and at the end of the room, behind high black control panels, with gleaming bus-bars and staring, gaping meters, a pair of generators hummed softly. The other end of the room was nearly all glass, and opened onto the patio and the swimming pool.

Mercer paused a moment, with his hand on the knob of the door, a strange light in his dark eyes.

“Now you’ll see why I called you here,” he said tensely. “You can judge for yourself whether the trip was worth while. Here she is!”

With a gesture he flung open the door, and I stared, following his glance, down at the great tiled swimming pool.

It is difficult for me to describe the scene. The patio was not large, but it was beautifully done. Flowers and shrubs, even a few small palms, grew in profusion in the enclosure, while above, through the movable glass roof--made in sections to disappear in fine weather--was the empty blackness of the sky.

None of the lights provided for the illumination of the covered patio was turned on, but all the windows surrounding the patio were aglow, and I could see the pool quite clearly.

The pool--and its occupant.

We were standing at one side of the pool, near the center. Directly opposite us, seated on the bottom of the pool, was a human figure, nude save for a great mass of tawny hair that fell about her like a silken mantle. The strangely graceful figure of a girl, one leg stretched out straight before her, the other drawn up and clasped by the interlocked fingers of her hands. Even in the soft light I could see her perfectly, through the clear water, her pale body outlined sharply against the jade green tiles.

I tore myself away from the staring, curious eyes of the figure.

“In God’s name, Mercer, what is it? Porcelain?” I asked hoarsely. The thing had an indescribably eery effect.

He laughed wildly.

“Porcelain? Watch... look!”

My eyes followed his pointing finger. The figure was moving. Gracefully it arose to its full height. The great cloud of corn-colored hair floated down about it, falling below the knees. Slowly, with a grace of movement comparable only with the slow soaring of a gull, she came toward me, walking on the bottom of the pool through the clear water as though she floated in air.

Fascinated, I watched her. Her eyes, startlingly large and dark in the strangely white face, were fixed on mine. There was nothing sinister in the gaze, yet I felt my body shaking as though in the grip of a terrible fear. I tried to look away, and found myself unable to move. I felt Mercer’s tense, sudden grip upon my arm, but I did not, could not, look at him.

“She--she’s smiling!” I heard him exclaim. He laughed, an excited, high-pitched laugh that irritated me in some subtle way.

She was smiling, and looking up into my eyes. She was very close now, within a few feet of us. She came still closer, until she was at my very feet as I stood on the raised ledge that ran around the edge of the pool, her head thrown back, staring straight up at me through the water.

I could see her teeth, very white between her coral-pink lips, and her bosom rising and falling beneath the veil of pale gold hair. She was breathing water!

Mercer literally jerked me away from the edge of the pool.

“What do you think of her, Taylor?” he asked, his dark eyes dancing with excitement.

“Tell me about it,” I said, shaking my head dazedly. “She is not human?”

“I don’t know. I think so. As human as you or I. I’ll tell you all I know, and then you can judge for yourself. I think we’ll know in a few minutes, if my plans work out. But first slip on a bathing suit.”

I didn’t argue the matter. I let Mercer lead me away without a word. And while I was changing, he told me all he knew of the strange creature in the pool.

“Late this afternoon I decided to go for a little walk along the beach,”

Mercer began. “I had been working like the devil since early in the morning, running some tests on what you call my thought-telegraph. I felt the need of some fresh sea air.

“I walked along briskly for perhaps five minutes, keeping just out of reach of the rollers and the spray. The shore was littered with all sorts of flotsam and jetsam washed up by the big storm, and I was just thinking that I would have to have a man with a truck come and clean up the shore in front of the place, when, in a little sandy pool, I saw--her.

“She was laying face down in the water, motionless, her head towards the sea, one arm stretched out before her, and her long hair wrapped around her like a half-transparent cloak.

“I ran up and lifted her from the water. Her body was cold, and deathly white, although her lips were faintly pink, and her heart was beating, faintly but steadily.

“Like most people in an emergency. I forgot all I ever knew about first aid. All I could think of was to give her a drink, and of course I didn’t have a flask on my person. So I picked her up in my arms and brought her to the house as quickly as I could. She seemed to be reviving, for she was struggling and gasping when I got here with her.

“I placed her on the bed in the guest room and poured her a stiff drink of Scotch--half a tumblerful, I believe. Lifting up her head, I placed the glass to her lips. She looked up me, blinking, and took the liquor in a single draught. She did not seem to drink it, but sucked it out of the glass in a single amazing gulp--that’s the only word for it. The next instant she was off the bed, her face a perfect mask of hate and agony.

“She came at me, hands clutching and clawing, making odd murmuring or mewing sounds in her throat. It was then that I noticed for the first time that her hands were webbed!”

“Webbed?” I asked, startled.

“Webbed,” nodded Mercer solemnly. “As are her feet. But listen, Taylor.

I was amazed, and not a little rattled when she came for me. I ran through the French windows out into the patio. For a moment she ran after me, rather awkwardly and heavily, but swiftly, nevertheless. Then she saw the pool.

“Apparently forgetting that I existed, she leaped into the water, and as I approached a moment later I could see her breathing deeply and gratefully, a smile of relief upon her features, as she lay upon the bottom of the pool. Breathing, Taylor, on the bottom of the pool! Under eight feet of water!”

“And then what, Mercer?” I reminded him, as he paused, apparently lost in thought.

“I tried to find out more about her. I put on my bathing suit and dived into the pool. Well, she came at me like a shark, quick as a flash, her teeth showing, her hands tearing like claws through the water. I turned, but not quickly enough to entirely escape. See?” Mercer threw back the dressing robe, and I saw a ragged tear in his bathing suit on his left side, near the waist. Through the rent three deep, jagged scratches were clearly visible.

“She managed to claw me, just once,” Mercer resumed, wrapping the robe about him again. “Then I got out and called on Carson for help. I put him into a bathing suit, and we both endeavored to corner her. Carson got two bad scratches, and one rather serious bite that I have bandaged.

I have a number of lacerations, but I didn’t fare so badly as Carson because I am faster in the water than he is.

“The harder we tried, the more determined I became. She would sit there, calm and placid, until one of us entered the water. Then she became a veritable fury. It was maddening.

“At last I thought of you. I phoned, and here we are!”

“But, Mercer, it’s a nightmare!” I protested. We moved out of the room.

“Nothing human can live under water and breathe water, as she does!”

Mercer paused a moment, staring at me oddly.

“The human race,” he said gravely, “came up out of sea. The human race as we know it. Some may have gone back.” He turned and walked away again, and I hurried after him.

“What do you mean. Mercer? ‘Some may have gone back?’ I don’t get it.”

Mercer shook his head, but made no other reply until we stood again on the edge of the pool.

The girl was standing where we had left her, and as she looked up into my face, she smiled again, and made a quick gesture with one hand. It seemed to me that she invited me to join her.

“I believe she likes you, Taylor,” said Mercer thoughtfully. “You’re light, light skin, light hair. Carson and I are both very dark, almost swarthy. And in that white bathing suit--yes, I believe she’s taken a fancy to you!”

Mercer’s eyes were dancing.

“If she has,” he went on, “it’ll make our work very easy.”

“What work?” I asked suspiciously. Mercer, always an indefatigable experimenter, was never above using his friends in the benefit of science. And some of his experiments in the past had been rather trying, not to say exciting.

“I think I have what you call my thought-telegraph perfected, experimentally,” he explained rapidly. “I fell asleep working on it at three o’clock, or thereabouts, this morning, and some tests with Carson seem to indicate that it is a success. I should have called you to-morrow, for further test. Nearly five years of damned hard work to a successful conclusion, Taylor, and then this mermaid comes along and makes my experiment appear about as important as one of those breakers rolling in out there!”

“And what do you plan to do now?” I asked eagerly, glancing down at the beautiful pale face that glimmered up at me through the clear water of the pool.

“Why, try it on her!” exclaimed Mercer with mounting enthusiasm. “Don’t you see, Taylor? If it will work on her, and we can direct her thoughts, we can find out her history, the history of her people! We’ll add a page to scientific history--a whole big chapter!--that will make us famous.

Man this is so big it’s swept me off my feet! Look!” And he held out a thin, aristocratic brown hand before my eyes, a hand that shook with nervous excitement.

“I don’t blame you,” I said quickly. “I’m no savant, and still I see what an amazing thing this is. Let’s get busy. What can I do?”

Mercer reached around the door into the laboratory and pressed a button.

“For Carson,” he explained. “We’ll need his help. In the meantime, we’ll look over the set-up. The apparatus is strewn all over the place.”

He had not exaggerated. The set-up consisted of a whole bank of tubes, each one in its own shielding copper box. On a much-drilled horizontal panel, propped up on insulators, were half a score of delicate meters of one kind and another, with thin black fingers that pulsed and trembled.

Behind the panel was a tall cylinder wound with shining copper wire, and beside it another panel, upright, fairly bristling with knobs, contact points, potentiometers, rheostats and switches. On the end of the table nearest the door was still another panel, the smallest of the lot, bearing only a series of jacks along one side, and in the center a switch with four contact points. A heavy, snaky cable led from this panel to the maze of apparatus further on.

“This is the control panel,” explained Mercer. “The whole affair, you understand, is in laboratory form. Nothing assembled. Put the different antennae plug into these jacks. Like this.”

He picked up a weird, hastily built contrivance composed of two semi-circular pieces of spring brass, crossed at right angles. On all four ends were bright silvery electrodes, three of them circular in shape, one of them elongated and slightly curved. With a quick, nervous gesture, Mercer fitted the thing to his head, so that the elongated electrode pressed against the back of his neck, extending a few inches down his spine. The other three circular electrodes rested on his forehead and either side of his head. From the center of the contrivance ran a heavy insulated cord, some ten feet in length, ending in a simple switchboard plug, which Mercer fitted into the uppermost of the three jacks.

“Now,” he directed, “you put on this one”--he adjusted a second contrivance upon my head, smiling as I shrank from the contact of the cold metal on my skin--”and think!”

He moved the switch from the position marked “Off” to the second contact point, watching me intently, his dark eyes gleaming.

Carson entered, and Mercer gestured to him to wait. Very nice old chap, Carson, impressive even in his bathing suit. Mercer was mighty lucky to have a man like Carson...

Something seemed to tick suddenly, somewhere deep in my consciousness.

“Yes, that’s very true: Carson is a most decent sort of chap.” The words were not spoken. I did not hear them, I knew them. What--I glanced at Mercer, and he laughed aloud with pleasure and excitement.

“It worked!” he cried. “I received your thought regarding Carson, and then turned the switch so that you received my thought. And you did!”

Rather gingerly I removed the thing from my head and laid it on the table.

“It’s wizardry, Mercer! If it will work as well on her...”

“It will, I know it will!--if we can get her to wear one of these,” replied Mercer confidently. “I have only three of them; I had planned some three-cornered experiments with you, Carson, and myself. We’ll leave Carson out of to-night’s experiment, however, for we’ll need him to operate this switch. You see, as it is now wired only one person transmits thoughts at a time. The other two receive. When the switch is on the first contact, Number One sends, and Numbers Two and Three receive. When the switch is on Number Two, then he sends thoughts, and Numbers One and Three receive them. And so on. I’ll lengthen these leads so that we can run them out into the pool, and then we’ll be ready.

Somehow we must induce her to wear one of these things, even if we have to use force. I’m sure the three of us can handle her.”

“We should be able to,” I smiled. She was such a slim, graceful, almost delicate little thing; the thought that three strong men might not be able to control her seemed almost amusing.

“You haven’t seen her in action yet,” said Mercer grimly, glancing up from his work of lengthening the cords that led from the antennae to the control panel. “And what’s more, I hope you don’t.”

I watched him in silence as he spliced and securely taped the last connection.

“All set,” he nodded. “Carson, will you operate the switch for us? I believe everything is functioning properly.” He surveyed the panel of instruments hastily, assuring himself that every reading was correct.

Then, with all three of the devices he called antennae in his hand, their leads plugged into the control panel, he led the way to the side of the pool.

The girl was strolling around the edge of the pool, feeling the smooth tile sides with her hands as we came into view, but as soon as she saw us she shot through the water to where we were standing.

It was the first time I had seen her move in this fashion. She seemed to propel herself with a sudden mighty thrust of her feet against the bottom; she darted through the water with the speed of an arrow, yet stopped as gently as though she had merely floated there.

As she looked up, her eyes unmistakably sought mine, and her smile seemed warm and inviting. She made again that strange little gesture of invitation.

With an effort I glanced at Mercer. There was something devilishly fascinating about the girl’s great, dark, searching eyes.

“I’m going in,” I said hoarsely. “Hand me one of your head-set things when I reach for it.” Before he could protest, I dived into the pool.

I headed directly towards the heavy bronze ladder that led to the bottom of the pool. I had two reasons in mind. I would need something to keep me under water, with my lungs full of air, and I could get out quickly if it were necessary. I had not forgotten the livid, jagged furrows in Mercer’s side.

Quickly as I shot to the ladder she was there before me, a dim, wavering white shape, waiting.

I paused, holding to a rung of the ladder with one hand. She came closer, walking with the airy grace I had noted before, and my heart pounded against my ribs as she raised one long, slim arm towards me.

The hand dropped gently on my shoulder, pressed it as though in token of friendship. Perhaps, I thought quickly, this was, with her, a sign of greeting. I lifted my own arm and returned the salutation, if salutation it were, aware of a strange rising and falling sound, as of a distant humming, in my ears.

The sound ceased suddenly, on a rising note, as though of inquiry, and it dawned on me that I had heard the speech of this strange creature.

Before I could think of a course of action, my aching lungs reminded me of the need of air, and I released my hold on the ladder and let my body rise to the surface.

As my head broke the water, a hand, cold and strong as steel, closed around my ankle. I looked down. The girl was watching me, and there was no smile on her face now.

“All right!” I shouted across the pool to Mercer, who was watching anxiously. Then, filling my lungs with air again, I pulled myself, by means of the ladder, to the bottom of the pool. The restraining hand was removed instantly.

The strange creature thrust her face close to mine as my feet touched bottom, and for the first time I saw her features distinctly.