Powell seized the ears and twisted the head. His mount turned ponderously. “Lead on, Macduff.” But he did not feel at all lighthearted.

The gigantic robots moved slowly, with mechanical precision, through the doorway that cleared their heads by a scant foot, so that the two men had to duck hurriedly, along a narrow corridor in which their unhurried footsteps boomed monotonously and into the air lock.

The long, airless tunnel that stretched to a pinpoint before them brought home forcefully to Powell the exact magnitude of the task accomplished by the First Expedition, with their crude robots and their start-from-scratch necessities. They might have been a failure, but their failure was a good deal better than the usual run of the System’s successes.

The robots plodded onward with a pace that never varied and with footsteps that never lengthened.

Powell said: “Notice that these tunnels are blazing with lights and that the temperature is Earth-normal. It’s probably been like this all the ten years that this place has remained empty.”

“How’s that?”

“Cheap energy; cheapest in the System. Sunpower, you know, and on Mercury’s Sunside, sunpower is something. That’s why the Station was built in the sunlight rather than in the shadow of a mountain. It’s really a huge energy converter. The heat is turned into electricity, light, mechanical work and what have you; so that energy is supplied and the Station is cooled in a simultaneous process.”

“Look,” said Donovan. “This is all very educational, but would you mind changing the subject? It so happens that this conversion of energy that you talk about is carried on by the photo-cell banks mainly—and that is a tender subject with me at the moment.”

Powell grunted vaguely, and when Donovan broke the resulting silence, it was to change the subject completely. “Listen, Greg. What the devil’s wrong with Speedy, anyway? I can’t understand it.”

It’s not easy to shrug shoulders in an insosuit, but Powell tried it. “I don’t know, Mike. You know he’s perfectly adapted to a Mercurian environment. Heat doesn’t mean anything to him and he’s built for the light gravity and the broken ground. He’s foolproof—or, at least, he should be.”

Silence fell. This time, silence that lasted.

“Master,” said the robot, “we are here.”

“Eh?” Powell snapped out of a semidrowse. “Well, get us out of here—out to the surface.”

They found themselves in a tiny substation, empty, airless, ruined. Donovan had inspected a jagged hole in the upper reaches of one of the walls by the light of his pocket flash.

“Meteorite, do you suppose?” he had asked.

Powell shrugged. “To hell with that. It doesn’t matter. Let’s get out.”

A towering cliff of a black, basaltic rock cut off the sunlight, and the deep night shadow of an airless world surrounded them. Before them, the shadow reached out and ended in knife-edge abruptness into an all-but-unbearable blaze of white light, that glittered from myriad crystals along a rocky ground.

“Space!” gasped Donovan. “It looks like snow.” And it did.