Pid maneuvered near the atomic power installation. He avoided the surrounding homes and hovered over a clump of woods.

Darkness fell, and the green planet's lone moon was veiled in clouds.

One cloud floated lower.

And landed.

"Quick, everyone out!" Pid shouted, detaching himself from the ship's controls. He assumed the Pilot's Shape best suited for running, and raced out the hatch. Ger and Ilg hurried after him. They stopped fifty yards from the ship, and waited.

Inside the ship a little-used circuit closed. There was a silent shudder, and the ship began to melt. Plastic dissolved, metal crumpled. Soon the ship was a great pile of junk, and still the process went on. Big fragments broke into smaller fragments, and split, and split again.

Pid felt suddenly helpless, watching his ship scuttle itself. He was a Pilot, of the Pilot caste. His father had been a Pilot, and his father before him, stretching back to the hazy past when the Grom had first constructed ships. He had spent his entire childhood around ships, his entire manhood flying them.

Now, shipless, he was naked in an alien world.

n a few minutes there was only a mound of dust to show where the ship had been. The night wind scattered it through the forest. And then there was nothing at all.

They waited. Nothing happened. The wind sighed and the trees creaked. Squirrels chirped, and birds stirred in their nests. An acorn fell to the ground.

Pid heaved a sigh of relief and sat down. The twenty-first Grom expedition had landed safely.

There was nothing to be done until morning, so Pid began to make plans. They had landed as close to the atomic power installation as they dared. Now they would have to get closer. Somehow, one of them had to get very near the reactor room, in order to activate the Displacer.

Difficult. But Pid felt certain of success. After all, the Grom were strong on ingenuity.

Strong on ingenuity, he thought bitterly, but terribly short of radioactives. That was another reason why this expedition was so important. There was little radioactive fuel left, on any of the Grom worlds. Ages ago, the Grom had spent their store of radioactives in spreading throughout their neighboring worlds, occupying the ones that they could live on.

Now, colonization barely kept up with the mounting birthrate. New worlds were constantly needed.

This particular world, discovered in a scouting expedition, was needed. It suited the Grom perfectly. But it was too far away. They didn't have enough fuel to mount a conquering space fleet.

Luckily, there was another way. A better way.

Over the centuries, the Grom scientists had developed the Displacer. A triumph of Identity Engineering, the Displacer allowed mass to be moved instantaneously between any two linked points.

One end was set up at Grom's sole atomic energy plant. The other end had to be placed in proximity to another atomic power source, and activated. Diverted power then flowed through both ends, was modified, and modified again.

Then, through the miracle of Identity Engineering, the Grom could step through from planet to planet; or pour through in a great, overwhelming wave.

It was quite simple.

But twenty expeditions had failed to set up the Earth-end Displacer.

What had happened to them was not known.

For no Grom ship had ever returned to tell.

efore dawn they crept through the woods, taking on the coloration of the plants around them. Their Displacers pulsed feebly, sensing the nearness of atomic energy.

A tiny, four-legged creature darted in front of them. Instantly, Ger grew four legs and