And what if Cook demanded specific information? Lucky had said to describe things, but what if Bigman accidentally failed to keep up the act? What if he tipped the boat and let slip the fact that Lucky had gone into the Sun-side? Lucky would never trust him again! With anything!

He put the thought aside. It would do him no good to concentrate on it

If there were only something to distract him. Something besides darkness and vacuum, besides the faint vibration of his own footsteps and the sound of his own breath.

He stopped to check his position in the main shaft. The side passages had letters and numbers ground sharply into their walls, and time had done nothing to dull their sharpness. Checking wasn't difficult.

However, the low temperature made the chart brittle and difficult to handle, and that didn't sweeten his mood. He turned his suit-light on his chest controls in order that he might adjust the dehumidifier. The inner surface of his face-plate was beginning to mist over faintly from the moisture in his breath, probably because the temperature within rose with his temper, he told himself.

He had just completed the adjustment when he moved his head sharply to one side as though he were suddenly cocking an ear to listen.

It was exactly what he was doing. He strained to sense the rhythm of faint vibration that he "heard" now only because his own steps had ceased.

He held his breath, remained as motionless as the rocky wall of the tunnel.

"Lucky?" he breathed into the transmitter. "Lucky?" The fingers of his right hand had adjusted the controls. The carrier wave was scrambled. No one else would make sense out of that light whisper. But Lucky would, and soon his voice would come in answer. Bigman was ashamed to admit to himself how welcome that voice would be.

"Lucky?" he said again.

The vibration continued. There was no answer.

Bigman's breathing quickened, first with tension, then with the savage joy born of excitement that always came over him when danger was in the offing.

There was someone else in the mines of Mercury with him. Someone other than Lucky.

Who, then? A Sirian? Had Lucky been right after all though he had thought he was merely putting up a smoke screen?

Maybe.

Bigman drew his blaster and put out his suit-light.

Did they know he was there? Were they coming to get him?

The vibrations weren't the blurred nonrhythmic "sound" of many people, or even two or three. To Bigman's keen ear, the distinctly separated "thrum-thrum" of vibration was the "sound" of one man's legs, rhythmically advancing.

And Bigman would meet any one man, anywhere, under any conditions.

Quietly, he put out his hand, touching the nearer wall. The vibrations sharpened noticeably. The other was in that direction then.

He moved forward quietly in the pitch-dark, his hand keeping a light touch on the wall. The vibrations being set up by the other were too intense, too careless. Either the other believed himself alone in the mines (as Bigman himself had until a moment before) or, if he were following Bigman, he wasn't wise in the ways of the vacuum.

Bigman's own footsteps had died to a murmur as he advanced catlike, yet the other's vibrations showed no change. Again, if the other had been following Bigman by sound, the sudden change in Bigman's progress should have been reflected in a change in the other's. It wasn't. The same conclusion, then as before.

He turned right at the next side-tunnel entrance and continued. His hand on the wall at once kept him along the way and guided him toward the other.

And then there was the blinding flash of a suit-light far ahead in the darkness as the motion of another's body whipped the beam across him. Bigman froze against the wall.

The light vanished. The other had passed across the tunnel Bigman was on. He was not advancing along it. Bigman hurried forward lightly. He would find that cross tunnel and then he would be behind the other.

They would meet then. He, Bigman, representing Earth and the Council of Science, and the enemy representing-whom?