yone
under me on the _Planetara_."

"What do you mean by that?" I demanded. "What--"

He interrupted me. "Just what I said."

Halsey smiled grimly. "What he means, Haljan, is that things are not
always what they seem these days. One cannot always tell a friend from
an enemy. The _Planetara_ is a public vessel. You have--how many is
it, Carter?--thirty or forty passengers this trip tonight?"

"Thirty-eight," said Carter.

"There are thirty-eight people listed for the flight to Ferrok-Shahn
tonight," Halsey said slowly. "And some may not be what they seem." He
raised his thin dark hand. "We have information...." He paused. "I
confess, we know almost nothing--hardly more than enough to alarm us."

Captain Carter interjected, "I want you and Dean to be on your guard.
Once on the _Planetara_ it is difficult for us to talk openly, but be
watchful. I will arrange for us to be doubly armed."

Vague, perturbing words! Halsey said, "They tell me George Prince is
listed for the voyage. I am suggesting, Haljan, that you keep your eye
especially on him. Your duties on the _Planetara_ leave you
comparatively free, don't they?"

"Yes," I agreed. With the first and second officers on duty, and the
Captain aboard, my routine was more or less that of an understudy.

I said, "George Prince? Who is he?"

"A mechanical engineer," said Halsey. "An underofficial of the Earth
Federated Catalyst Corporation. But he associates with bad
companions--particularly Martians."

I had never heard of this George Prince, though I was familiar with
the Federated Catalyst Corporation, of course. A semigovernment trust,
which controlled virtually the entire Earth supply of radiactum, the
catalyst mineral which was revolutionizing industry.

"He was in the Automotive Department," Carter put in. "You've heard of
the Federated Radiactum Motor?"

We had, of course. It was a recent Earth discovery and invention. An
engine of a new type, using radiactum as its fuel.

Snap demanded, "What in the stars has this got to do with Johnny
Grantline?"

"Much," said Halsey quietly, "or perhaps nothing. But George Prince
some years ago mixed in rather unethical transactions. We had him in
custody once. He is known as unusually friendly with several Martians
in Greater New York of bad reputation."

"Well?"

"What you don't know," Halsey said, "is that Grantline expects to find
radiactum on the Moon."

We gasped.

"Exactly," said Halsey. "The ill-fat