queer ache came into his heart. Something made him think of a white tower in the red hills near Helion, and a girl waiting in its fragrant garden of saffron and purple—a girl like this.

The body lay upon a bed of blazing jewels.

It appeared, Thad thought, as if the pile of gems upon the floor had been hastily scraped from the coffer, to make room for the quiet form. He wondered how long it had lain there. It looked as if it might have been living but minutes before. Some preservative....

His thought was broken by a sound that rang from the open hatchway on the deck above—the furious barking and yelping of the dog. Abruptly that was silent, and in its place came the uncanny and terrifying scream that Thad had heard once before, on this flier of mystery. A shriek so keen and shrill that it seemed to tear out his nerves by their roots. The voice of the haunter of the ship.

When Thad came back upon the deck, the dog was still barking nervously. He saw the animal forward, almost at the bow. Hackles raised, tail between its legs, it was slinking backward, barking sharply as if to call for aid.

Apparently it was retreating from something between Thad and itself. But Thad, searching the dimly-lit deck, could see no source of alarm. Nor could the structures upon it have shut any large object from his view.

"It's all right!" Thad called, intending to reassure the frightened animal, but finding his voice queerly dry. "Coming on the double, old man. Don't worry."

The dog had reached the end of the deck. It stopped yelping, but snarled and whined as if in terror. It began darting back and forth, moving exactly as if something were slowly closing in upon it, trapping it in the corner. But Thad could see nothing.

Then it made a wild dash back toward Thad, darting along by the wall, as if trying to run past an unseen enemy.

Thad thought he heard quick, rasping footsteps, then, that were not those of the dog. And something seemed to catch the dog in mid-air, as it leaped. It was hurled howling to the deck. For a moment it struggled furiously, as if an invisible claw had pinned it down. Then it escaped, and fled whimpering to Thad's side.

He saw a new wound across its hips. Three long, parallel scratches, from which fresh red blood was trickling.

Regular scraping sounds came from the end of the deck, where no moving thing was to be seen—sounds such as might be made by the walking of feet with unsheathed claws. Something was coming back toward Thad. Something that was invisible!

Terror seized him, with the knowledge. He had nerved himself to face desperate men, or a savage animal. But an invisible being, that could creep upon him and strike unseen! It was incredible ... yet he had seen the dog knocked down, and the bleeding wound it had received.

His heart paused, then beat very quickly. For the moment he thought only blindly, of escape. He knew only an overpowering desire to hide, to conceal himself from the invisible thing. Had it been possible, he might have tried to leave the flier.

Beside him was one of the companionways amidships, giving access to a compartment of the vessel that he had not explored. He turned, leaped down the steps, with the terrified dog at his heels.

Below, he found himself in a short hall, dimly lighted. Several metal doors opened from it. He tried one at random. It gave. He sprang through, let the dog follow, closed and locked it.

Trying to listen, he leaned weakly against the door. The rushing of his breath, swift and regular. The loud hammer of his thudding heart. The dog's low whines. Then—unmistakable scraping sounds, outside.

The scratching of claws, Thad knew. Invisible claws!

He stood there, bracing the door with the weight of his body, holding the welding arc ready in his hand. Several times the hinges creaked, and he felt a heavy pressure against the panels. But at last the scratching sounds ceased. He relaxed. The monster had withdrawn, at least for a time.

When he had time to think, the invisibility of the thing was not so incredible. The mounted creatures he had seen in the hold were evidence that the flier had visited some unknown planet, where weird life reigned. It was not beyond reason that such a planet should be inhabited by beings invisible to human sight.

Human vision, as he knew, utilizes only a tiny fraction of the spectrum. The creature must be largely transparent to visible light, as human flesh is radiolucent to hard X-rays. Quite possibly it could be seen by infra-red or ultra-violet light—evidently it was visible enough to the dog's eyes, with their different range of sensitivity.

Pushing the subject from his mind, he turned to survey the room into which he had burst. It had apparently been occupied by a woman. A frail blue silk dress and more intimate items of feminine wearing apparel were hanging above the berth. Two pairs of delicate black slippers stood neatly below it.

Across from him was a dressing table, with a large mirror above it. Combs, pins, jars of cosmetic cluttered it. And Thad saw upon it a little leather-bound book, locked, stamped on the back "Diary."

He crossed the room and picked up the little book, which smelled faintly of jasmine. Momentary shame overcame him at thus stealing the secrets of an unknown girl. Necessity, however, left him no choice but to seize any chance of learning more of this ship of mystery and her invisible haunter. He broke the flimsy fastening.

Linda Cross was the name written on the fly-leaf, in a firm, clear feminine hand. On the next page was the photograph, in color, of a girl, the brown-haired girl whose body Thad had discovered in the crystal coffer in the hold. Her eyes, he saw, had been blue. He thought she looked very lovely—like the waiting girl in his old dream of the silver tower in the red hills by Helion.

The diary, it appeared, had not been kept very devotedly. Most of the pages were blank.

One of the first entries, dated a year and a half before, told of a party that Linda had attended in San Francisco, and of her refusal to dance with a certain man, referred to as "Benny," because he had been unpleasantly insistent about wanting to marry her. It ended:

"Dad said to-night that we're going off in the Dragon again. All the way to Uranus, if the new fuel works as he expects. What a lark, to explore a few new worlds of our own! Dad says one of Uranus' moons is as large as Mercury. And Benny won't be proposing again soon!"

Turning on, Thad found other scattered entries, some of them dealing with the preparation for the voyage, the start from San Francisco—and a huge bunch of flowers from "Benny," the long months of the trip through space, out past the orbit of Mars, above the meteor belt, across Jupiter's orbit, beyond the track of Saturn, which was the farthest point that rocket explorers had previously reached, and on to Uranus, where they could not land because of the unstable surface.

The remainder of the entries Thad found less frequent, shorter, bearing the mark of excitement: landing upon Titania, the third and largest satellite of Uranus; unearthly forests, sheltering strange and monstrous life; the hunting of weird creatures, and mounting them for museum specimens.

Then the discovery of a ruined city, whose remains indicated that it had been built by a lost race of intelligent, spiderlike things; the finding of a temple whose walls were of precious metals, containing a crystal chest filled with wondrous gems; the smelting of the metal into convenient ingots, and the transfer of the treasure to the hold.

The first sinister note there entered the diary:

"Some of the men say we shouldn't have disturbed the temple. Think it will bring us bad luck. Rubbish, of course. But one man