"Down," she said as they walked toward it. "And there's some machinery or something down there. I heard it. Or maybe I only felt the vibrations. It throbs, anyway."

"Probably the generator for the school's lighting system. Did you go down and look?"

"No."

"All right, then." He opened the door. "Down we go."

At the bottom of a flight of steps there was a corridor lit by dim electric light bulbs along one wall. The corridor became a tunnel, sloping gradually downward. They had been going north, Don judged, but then the tunnel made a right turn and now they were following it due east. "I don't hear any throbbing," he said.

"Well, I did, and from way up here. They must have turned it off."

"How long ago was that?"

"An hour, maybe."

"While we were still rising. That would make sense. We've stopped again, you know. Professor Garet gave us a bulletin on it."

He had been going ahead of her in the narrow tunnel. Now it widened and they were able to walk side by side. There seemed to be no end to it.

But then they came to a st.u.r.dy-looking door, padlocked.

"That's that," Don said.

"That's that nothing," she said. "Break it down."

He laughed. "You flatter me. Come on back."

"Don't you think this is at all peculiar? A tunnel starting under an abandoned grandstand, running all this way and ending in a locked door?"

"Maybe this was a station on the underground railway. It looks old enough."

"We're going through that door." She opened her purse and took out a key ring. On it was an extensive collection of keys. Eventually she found one that opened the padlock.

"Well!" he said. "Who taught you _that_?"

"Open the door."

The corridor beyond the door was lined--walls, ceiling and floor--with a silvery metal. It continued east a hundred yards or so, swung north and then went east again, widening all the time.

It ended in a great room whose far wall was gla.s.s or some equally transparent substance. The room was a huge observatory at the end of Superior but below its rim. They could look down from it, not without a touch of nausea, to the Earth four miles below.

Don, thinking of the surface of Superior above, thought it was as if they were looking out of the gondola slung beneath a dirigible.

Or from one of the lower portholes in a giant flying saucer.

V

There were clouds below that occasionally hid the Earth from sight. For a minute or more they gazed in silence at the magnificent view.

"This wasn't built in a day," Jen Jervis said at last.

"I should say not," Don agreed. "Millions of years."

She looked at him sharply. "I wasn't talking about the age of the Earth.

I mean this room--this lookout post--whatever it is."

He grinned at her. "I agree with you there, too. I'm really a very agreeable fellow, Miss Jervis. Obviously, whoever built it knew well in advance that Superior was going to take off. They also knew how much of it was going up and exactly where this would have to be built so it would be at the edge."

"Under the edge, you mean, with a downward view."

"That's right. From a distance I'd say Superior looked as if someone had cut the end off an orange. The flat part--where the cut was made--is the surface and we're looking out from a piece of the convex skin."

"You put things so simply, Mr. Cort, that even a child could understand," she said acidly.

"Thank you," he said complacently. He had remembered that whoever was listening in for Military Intelligence through the tiny radio under his shirt could have only a vague idea of what was going on. Any little word pictures he could supply, therefore, would help them understand. He had to risk the fact that his companion might think him a bit of an idiot.

Of course with this Geneva Jervis it was easy to lay himself open to the scathing comment and the barbed retort. He imagined she was extremely useful in her role as Girl Friday to Senator Bobby Thebold.

"I don't think this is the work of those b.o.o.bies at the b.o.o.by hatch,"

she was saying.

"I beg your pardon?"

"The Cavalier Inst.i.tution of Applied Foolishness, whatever they call it.

They just wouldn't be capable of an undertaking of this scope."

"Oh, I agree. That's why I let you drag me away from the meeting. It was a lot of pseudo-scientific malarkey. Old Doc Rubach, D.V.M., was going on about the ultimote being connected to the thighbone, way up in the middle of the air. Tell me, who do _you_ think is behind it all?"

She was walking around the big-sided room as if taking mental inventory.

There wasn't much to catalogue--six straight chairs, heavy and modern-looking, with a large wooden table, a framed piece of dark gla.s.s that might be a television set, and a gray steel box about the size and shape of a three-drawer filing cabinet. This last was near the big window-wall and had three black b.u.t.tons on its otherwise smooth top. Don itched to push the b.u.t.tons to see what would happen. Jen Jervis seemed to have the same urge. She drummed on the box with her long fingernails.

"I?" she said. "Behind it all?"

"Yes. What's your theory? Is this something for the Un-Earthly Activities Committee to investigate?"

"Don't be impertinent. If the Senator thinks it's his duty to look into it, he will. He undoubtedly is already. In the meantime, I can do no less than gather whatever information I can while I'm on the scene."

"Very patriotic. What do you conclude from your information-gathering so far?"

"Obviously there's some kind of conspiracy--" she began, then stopped as if she suspected a trap.

"--afoot," Don said with a grin. "As I see it, all you do is have Bobby the Bold subpoena everybody up here--every last man-jack of 'em--to testify before his committee. They wouldn't dare refuse."

"I don't find you a bit amusing, Mr. Cort, though I have no doubt this soph.o.m.oric humor makes a big hit with your teen-age blonde. We'd better get back. I can see it was a mistake to expect any co-operation from you."