s sooner or later and we
have to be ready for him."

He glanced at the new radar screen they had set up that morning beside
the bank of other controls. Any ship coming within a hundred miles of
the laboratory would be detected instantly and pinpointed.

The board flashed now. In the screen they saw a huge passenger ship
spearing down toward the airport south of them.

"With the port that close," said Russ, "we'll get a lot of signals."

"I ordered the Belgium factory to rush work on the ship," said Greg.
"But it will be a couple of weeks yet. We just have to sit tight and
wait. As soon as we have the ship we'll start in on Chambers; but until
we get the ship, we just have to dig in and stay on the defensive."

He studied the scene in the screen. The ship had leveled off, was
banking in to the port. His eyes turned away, took in the laboratory
with its crowding mass of machinery.

"We don't want to fool ourselves about Chambers," he said. "He may not
have the power here on Earth that he does on the other planets, but he's
got plenty. Feeling the way he does, he'll try to finish us off in a
hurry now."

Russ reached out to the table that stood beside the bank of controls and
picked up a small, complicated mechanism. Its face bore nine dials, with
the needles on three of them apparently registering, the other six
motionless.

"What is that?" asked Greg.

"A mechanical detective," said Russ. "A sort of mechanical shadow. While
you were busy with the stock market stunt, I made several of them. One
for Wilson and another for Chambers and still another for Craven." He
hoisted and lowered the one in his hand. "This one is for Stutsman."

"A shadow?" asked Greg. "Do you mean that thing will trail Stutsman?"

"Not only trail him," said Russ. "It will find him, wherever he may be.
Some object every person wears or carries is made of iron or some other
magnetic metal. This 'shadow' contains a tiny bit of that ridiculous
military decoration that Stutsman never allows far away from him. Find
that decoration and you find Stutsman. In another one I have a chunk of
Wilson's belt buckle, that college buckle, you know, that he's so proud
of. Chambers has a ring made of a piece of meteoric iron and that's the
bait for another machine. Have a tiny piece off Craven's spectacles in
his machine. It was easy to get the stuff. The force field enables a man
to reach out and take anything he wants to, from a massive machine to a
micro