_"Dr. Brende, see P.C.S. 10.42, warning you, probably of Venus
immigrants now here. Do you need guard? Or will you come to Washington
at once for personal safety?"_

"Father!" cried Elza.

Georg burst out. "Enough of this. We cannot--dare not talk in here.
Father, come----"

We went out into the corridor again, across which was the small room
insulated from all aerial vibrations. In the corridor a figure was
standing--the one other member of the Brende household--the
maid-servant, a girl about Elza's age. I knew her well, of course, but
this evening I had forgotten her existence. She was standing in the
corridor. Did I imagine it, or had she been gazing up at the mechanism
ten feet above the floor--the mechanism controlling the insulated room?

"You wish me, Miss Elza? I thought I heard you call."

"No, Ahla, not 'til later."

With a gesture of respect, the girl withdrew, passing from our sight
down the incline which led to the lower part of the house.

It was a very small incident, but in view of what was transpiring, it
gave me a shock nevertheless.

For Elza's maid was a Venus girl!

CHAPTER III

_Spy in the House_

The insulated room was small, with a dome-shaped ceiling, no windows,
and but one small, heavy door through which we entered, closing it
carefully behind us.

"At last," Dr. Brende exclaimed. "Now we can talk freely."

But I was not satisfied. "That girl, Ahla--can you trust her?"

They all looked at me in surprise. When one is close to danger,
sometimes one recognizes it least; with Ahla in this household for over
a year now, they could not imagine her an enemy.

"I saw her looking up at the insulator," I added swiftly. "Out there in
the corridor. Am I talking wild? Perhaps I am. But she seemed startled;
and she was standing just under the insulator, wasn't she?"

"But--" began Elza.

"Wait," I exclaimed. "When I first saw the President fall, at Park
Sixty, I felt that a Venus man had done it. These other murders--they're
all the same. Done by Venus men of the Cold Country."

"Ahla's country," Elza murmured.

"Yes. Exactly. And the Venus Central State has been attacked and has
fallen. An assassination on Mars, and three here on Earth--all
simultaneously. It's one gigantic plot, I tell you--and the Cold Country
of Venus is at the bottom of it."

Georg jumped to his feet. "I'll see if the room has been tampered with."

He was back presently. "The insulator is intact. I s