rocket which, up to then, had doubled as a lifeboat.

The schedule called for him to make a rough three-hour scouting survey
in an ever-widening spiral from our dome. This had been regarded as a
probable waste of time, rocket fuel and manpower--but a necessary
precaution. He was supposed to watch for such things as bug-eyed
monsters out for a stroll on the Lunar landscape. Basically, however,
Tom's survey was intended to supply extra geological and astronomical
meat for the report which Monroe was to carry back to Army HQ on Earth.

Tom was back in forty minutes. His round face, inside its transparent
bubble helmet, was fish-belly white. And so were ours, once he told us
what he'd seen.

He had seen another dome.

"The other side of Mare Nubium--in the Riphaen Mountains," he babbled
excitedly. "It's a little bigger than ours, and it's a little flatter on
top. And it's not translucent, either, with splotches of different
colors here and there--it's a dull, dark, heavy gray. But that's all
there is to see."

"No markings on the dome?" I asked worriedly. "No signs of anyone--or
anything--around it?"

"Neither, Colonel." I noticed he was calling me by my rank for the first
time since the trip started, which meant he was saying in effect, "Man,
have you got a decision to make!"

"Hey, Tom," Monroe put in. "Couldn't be just a regularly shaped bump in
the ground, could it?"

"I'm a geologist, Monroe. I can distinguish artificial from natural
topography. Besides--" he looked up--"I just remembered something I left
out. There's a brand-new tiny crater near the dome--the kind usually
left by a rocket exhaust."

"Rocket exhaust?" I seized on that. "_Rockets_, eh?"

* * * * *

Tom grinned a little sympathetically. "Spaceship exhaust, I should have
said. You can't tell from the crater what kind of propulsive device
these characters are using. It's not the same kind of crater our
rear-jets leave, if that helps any."

Of course it didn't. So we went into our ship and had a council of war.
And I do mean war. Both Tom and Monroe were calling me Colonel in every
other sentence. I used their first names every chance I got.

Still, no one but me could reach a decision. About what to do, I mean.

"Look," I said at last, "here are the possibilities. They know we are
here--either from watching us land a couple of hours ago or from
observing Tom's scout-ship--or they do not know we are here. They