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 The monster had withdrawn, at least for a time.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.

P

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 

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