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.

W

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.

T

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 

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