"We're being followed. Did you hear anything?"

"No!" Yet I thought now that I could hear something. Vague footfalls.
A rustling. And a microscopic whine, as though some device were within
range of us.

Snap was fumbling in his pocket. "Wait! I've got a pair of low-scale
detectors."

He put the little grids against his ears. I could hear the sharp
intake of his breath. Then he seized me, pulled me down to the metal
floor of the entryway.

"Back, Gregg! Get back!" I could barely hear his whisper. We crouched
as far back into the doorway as we could get. I was armed. My official
permit for the carrying of the pencil heat ray allowed me always to
have it with me. I drew it now. But there was nothing to shoot at. I
felt Snap clamping the grids on my ears. And now I heard something! An
intensification of the vague footsteps I had thought I heard before.

There was something following us! Something out in the corridor there
now! The corridor was dim, but plainly visible, and as far as I could
see it was empty. But there was something there. Something invisible!
I could hear it moving. Creeping toward us. I pulled the grids off my
ears.

Snap murmured, "You've got a local phone?"

"Yes. I'll get them to give us the street glare!"

I pressed the danger signal, giving our location to the operator. In a
second we got the light. The street in all this neighborhood burst
into a brilliant actinic glare. The thing menacing us was revealed! A
figure in a black cloak, crouching thirty feet away across the
corridor.

Snap was unarmed but he flung his hands out menacingly. The figure,
which may perhaps not have been aware of our city safeguard, was taken
wholly by surprise. A human figure, seven feet tall at the least, and
therefore, I judged, a Martian man. The black cloak covered his head.
He took a step toward us, hesitated, and then turned in confusion.

Snap's shrill voice was bringing help. The whine of a street guard's
alarm whistle nearby sounded. The figure was making off! My pencil ray
was in my hand and I pressed its switch. The tiny heat ray stabbed
through the air, but I missed. The figure stumbled but did not fall. I
saw a bare gray arm come from the cloak, flung up to maintain its
balance. Or perhaps my pencil ray had seared his arm. The gray-skinned
arm of a Martian.

Snap was shouting, "Give him another!" But the figure passed beyond
the actinic glare and vanished.

We were detained in the turmoil of the