ck three miles long and a
mile wide and over six hundred feet in height."

"Three men! How on earth did you do it?"

"Two men and one mole. We did it with a ray, the secret of which only
the Selom and Saranoff know."

* * * * *

"You have told me a disintegrating ray is an impossibility," objected
Carnes.

"It is. This was not a disintegrating ray. Carnes, either I am crazy
or the Selom have solved the secret of time, the fourth dimension. I
haven't been able to grasp the whole thing yet. What I think we did
was to remove that rock a distance, perhaps only a millionth of a
second, forward or back into time. At any rate it ceased to exist, yet
they can bring it back unchanged at will. That was the way they
captured our plane. They sent out a magnetic ray of such power that it
stopped our plane in midair and brought it to the ground. They
removed the rock from beneath us and lowered us into the hole. By
reversing the process they restored things to their original
condition. All of these tunnels and rooms were made in that way."

"I still don't understand how they did it."

"I don't either, but I hope to in time. Now let's go to bed. It's
late. To-morrow you will start your lessons with Captain Garland as an
instructor. He won't know you for he was operated on this afternoon.
Do your best to become a pilot. When I get ready, I want you with me
in full possession of all your faculties."

The next morning the two prisoners separated and went to their duties.
In the cavern which Dr. Bird had described, Captain Garland was
waiting beside the plane he had flown. He did not know Carnes, but he
still knew how to fly. Declining to enter into any conversation, he
started expounding the theory of flying to the detective. Carnes
remembered Dr. Bird's words and applied himself wholeheartedly. For
four hours they worked together. At the end of that time the light
faded in the cavern and Carnes was led by an unseen guide back to his
cell. He threw himself on a bed and awaited Dr. Bird's return.

"I have learned a few more things about the Selom," said the doctor
when he entered the cell several hours later. "We are in their largest
community. They have cities or warrens scattered all over the world.
Each city has its own ruler, but the whole race are ruled by an
overlord or king who habitually lives here. He is away visiting a
community under northern Africa just now, but he will be back in a fe