Inside the trailer, nothing happened. Lane went grimly through it, making sure there was no opening to the outer air. The ventilator above the small cook-stove was open. He closed it. The result of these precautions was stifling heat, but Lane felt cold chills down his spine simply by thinking of invisible stranglers trying to worm their way in to where the three humans were. There were times, too, when a deep and bitter rage took possession of him.

“Be still!” said Professor Warren irritably, as she paced up and down the confined space of the trailer’s living section. “You make me hot to look at you! I have to think things out. Either we are all quite insane, or the people who used to own the Monster were much more sensible than we’ve been!”

Carol sat quietly, looking from one to the other—her buxom aunt in khaki riding breeches, and Lane seething in citified tweeds. Outside the trailer there was a rocky shelf which loomed over a valley to the east.

“They said that things sat on their chests and stopped their breaths,” Professor Warren went on, “so they ducked under the covers and the ha’nts went away. I was scornful! But now I think that they may have been right!”

Lane forced himself to sit down. He lighted a cigarette. “There was something that tried to strangle me,” he said savagely, “and it whined while it did so. I heard the same sound just outside, and the dog saw something. But whatever attacked me and the Monster was invisible! And that’s impossible! Real things can’t be invisible!”