The lieutenant started out of the door. Sergeant Bellews followed at
leisure. He painstakingly avoided ever walking the regulation two paces
behind a commissioned officer. Either he walked side by side, chatting,
or he walked alone. Wise officers let him get away with it.

* * * * *

Reaching the open air a good twenty yards behind the lieutenant, he
cocked an approving eye at a police-up unit at work on the lawn outside.
Only a couple of weeks before, that unit had been in a bad way. It
stopped and shivered when it encountered an unfamiliar object.

But now it rolled across the grass from one path-edge to another. When
it reached the second path it stopped, briskly moved itself its own
width sidewise, and rolled back. On the way it competently manicured the
lawn. It picked up leaves, retrieved a stray cigarette-butt, and snapped
up a scrap of paper blown from somewhere. Its tactile units touched a
new-planted shrub. It delicately circled the shrub and went on upon its
proper course.

* * * * *

Once, where the grass grew taller than elsewhere, it stopped and
whirred, trimming the growth back to regulation height. Then it went on
about its business as before.

Sergeant Bellews felt a warm sensation. That was a good machine that had
been in a bad way and he'd brought it back to normal, happy operation.
The sergeant was pleased.

The lieutenant turned into the Communications building. Sergeant Bellews
followed at leisure. A jeep went past him--one of the special jeeps
being developed at this particular installation--and its driver was
talking to someone in the back seat, but the jeep matter-of-factly
turned out to avoid Sergeant Bellews. He glowed. He'd activated it.
Another good machine, gathering sound experience day by day.

He went into the room where Betsy stood--the communicator which, alone
among receiving devices in the whole world, picked up the enigmatic
broadcasts consistently. Betsy was a standard Mark IV communicator, now
carefully isolated from any aerial. She was surrounded by recording
devices for vision and sound, and by the most sensitive and complicated
instruments yet devised for the detection of short-wave radiation.
Nothing had yet been detected reaching Betsy, but something must. No
machine could originate what Betsy had been exhibiting on her screen and
emitting from her speakers.

Sergeant Bellews tensed instantly. Betsy's s