hing was moving! Footsteps moving away from me
down the deck! I followed; and suddenly I was running. Chasing
something I could hear, but could not see. It turned into the smoking
room.

I burst in. And a real sound smothered the phantom. Johnson the purser
was sitting here alone in the dimness. He was smoking. I noticed that
his cigar held a long frail ash. It could not have been him I was
chasing. He was sitting there quite calmly. A thick-necked, heavy
fellow, easily out of breath. But he was breathing calmly now.

He sat up in amazement at my wild-eyed appearance, and the ash jarred
from his cigar.

"Gregg! What in the devil--"

I tried to grin. "I'm on my way to bed--worked all night helping
Snap."

I went past him, out the door into the main corridor. It was the only
way the invisible prowler could have gone. But I was too late now--I
could hear nothing. I dashed forward into the main lounge. It was
empty, dim and silent, a silence broken presently by a faint click, a
stateroom door hastily closing. I swung and found myself in a tiny
transverse passage. The twin doors of A20 and A22 were before me.

The invisible eavesdropper had gone into one of these rooms! I
listened at each of the panels, but there was only silence within.

The interior of the ship was suddenly singing with the steward's
siren--the call to awaken the passengers. It startled me. I moved
swiftly away. But as the siren shut off, in the silence I heard a
soft, musical voice:

"Wake up, Anita, I think that's the breakfast call."

And her answer, "All right, George."

IV

I did not appear at that morning meal. I was exhausted and drugged
with lack of sleep. I had a moment with Snap to tell him what had
occurred. Then I sought out Carter. He had his little chart room
insulated. And we were cautious. I told him what Snap and I had
learned: the rays from the Moon, proving that Grantline had
concentrated a considerable ore body. I also told him of Grantline's
message.

"We'll stop on the way back, as he directs, Gregg." He bent closer to
me. "At Ferrok-Shahn I'm going to bring back a cordon of
Interplanetary Police. The secret will be out, of course, when we stop
at the Moon. We have no right, even now, to be flying this vessel as
unguarded as it is."

He was very solemn. And he was grim when I told him of the invisible
eavesdropper.

"You think he overheard Grantline's message? Who was it? You seem to
feel it was George Pri