derground tunnel. Shall we try it?"

"Yes, if you think the Princess Tina and that man Larry is there."

"I am seeking Tugh. Will you kill him if we find him?"

"Yes," I assured him.

Rash promise!

* * * * *

Migul was leading me between the rows of unattended machinery to the
cavern's opposite side. It said, once:

"There have been too many recent vibrations here: I cannot pick Tugh's
trail. It is quicker to go where he might have been recently; there I
will try to find his vibrations."

We came to the entrance of a tunnel. It was the cross passage leading
to the cellar corridors of the palace five hundred feet away. It
seemed deserted, and was very dimly illumined by hidden lights. I
followed the great metal figure of Migul, which stalked with
stiff-legged steps in advance of me. The arch of the tunnel-roof
barely cleared the top of Migul's square-capped head.

My hand was in the side pocket of my jacket, my fingers gripping the
ray cylinder for instant action. But it was a singularly ineffectual
weapon for me under the circumstances, in spite of the sense of
security it gave me. I could only use the cylinder against a
human--and, save Tugh, it was the Robots, not the humans who were my
enemies!

We had gone no more than a hundred feet or so when Migul slowed our
pace, and began to walk stooped over, with one of its abnormally long
arms held close to the ground. The fingers were stiffly outstretched
and barely skimmed the floor surface of the tunnel. As we passed
through a spot of light I saw that Migul had extended from each of
the fingertips an inch-long filament of wire, like finger nails.

The Robot murmured abruptly, "Tugh's vibrations are here. I can feel
them. He has passed this way recently."

* * * * *

Tugh's trail! I knew then that Tugh's body, touching this ground, had
altered to some infinitesimal degree the floor-substance's inherent
vibration characteristics. Vibrations of every sort are communicable
from one substance to another. Tugh's trail was here--his
vibration-scent--and like a hound with his nose to the ground, Migul's
fingers with the extended filaments were feeling it. What strange
sensitivity! What an amazing development of science was manifested in
every move and act and word of this Robot! Yet, in my own Time-world
of 1935, it was all crudely presaged: this now before me was merely
the culmination.

"He recent