because I have decided that the life of my daughter is less important than the lives of many thousands of people.

"I appeal to you, Gray, to let her go. Her life won't save you. And it's very precious to me."

Caron's ship swept over, low above the cables, and the grinding concussion of a bomb lifted the ship, hurled it down with the stern end twisted to uselessness. The screen went dead.

Gray caught the half stunned girl. "I wish to heaven I could get rid of you!" he grated. "And I don't know why I don't!"

But she was with him when he set out down the valley, making for the cliff caves, up where the copper cables were anchored.

Caron's ship, a fast, small fighter, wheeled between the cliffs and turned back. Gray dropped flat, holding the girl down. Bombs pelted them with dirt and uprooted vegetables, started fires in the wheat. The pilot found a big enough break in the cables and came in for a landing.

Gray was up and running again. He knew the way into the explored galleries. From there on, it was anybody's guess.

Caron was brazen enough about it. The subtle way had failed. Now he was going all out. And he was really quite safe. With the broken cables to act as conductors, the first thunderstorm would obliterate all proof of his activities in this valley. Mercury, because of its high electrical potential, was cut off from communication with other worlds. Moulton, even if he had knowledge of what went on, could not send for help.

Gray wondered briefly what Caron intended to do in case he, Gray, made good his escape. That outpost in the p. 64 main valley, for which Ward had been heading, wasn't kept for fun. Besides, Caron was too smart to have only one string to his bow.

Shouts, the spatter of shots around them. The narrow trail loomed above. Gray sent the girl scrambling up.

The sun burst up over the high peaks, leaving the black shadow of the valley still untouched. Caron's ship roared off. But six of its crew came after Gray and Jill Moulton.

The chill dark of the tunnel mouth swallowed them. Keeping right to avoid the great copper posts that held the cables, strung through holes drilled in the solid rock of the gallery's outer wall, Gray urged the girl along.

The cleft his hand was searching for opened. Drawing the girl inside, around a jutting shoulder, he stopped, listening.

Footsteps echoed outside, grew louder, swept by. There was no light. But the steps were too sure to have been made in the dark.

"Infra-red torches and goggles," Gray said tersely, "You see, but your quarry doesn't. Useful gadget. Come on."

"But where? What are you going to do?"

"Escape, girl. Remember? They smashed my ship. But there must be another one on Mercury. I'm going to find it."

"I don't understand."

"You probably never will. Here's where I leave you. That Martian Galahad will be along any minute. He'll take you home."

Her voice came soft and puzzled through the dark.

"I don't understand you, Gray. You wouldn't risk my life. Yet you're turning me loose, knowing that I might save you, knowing that I'll hunt you down if I can. I thought you were a hardened cynic."

"What makes you think I'm not?"

"If you were, you'd have kicked me out the waste tubs of the ship and gone on. You'd never have turned back."

"I told you," he said roughly, "I don't kill women." He turned away, but her harsh chuckle followed him.

"You're a fool, Gray. You've lost truth—and you aren't even true to your lie."

He paused, in swift anger. Voices the sound of running men, came up from the path. He broke into a silent run, following the dying echoes of Caron's men.

"Run, Gray!" cried Jill. "Because we're coming after you!"

The tunnels, ancient blowholes for the volcanic gases that had tortured Mercury with the raising of the titanic mountains, sprawled in a labyrinthine network through those same vast peaks. Only the galleries lying next the valleys had been explored. Man's habitation on Mercury had been too short.

Gray could hear Caron's men circling about through connecting tunnels, searching. It proved what he had already guessed. He was taking a desperate chance. But the way back was closed—and he was used to taking chances.

The geography of the district was clear in his mind—the valley he had just left and the main valley, forming an obtuse angle with the apex out on the wind-torn plain and a double range of mountains lying out between the sides of the triangle.

Somewhere there was a passage through those peaks. Somewhere there was a landing place, and ten to one there was a ship on it. Caron would never have left his men stranded, on the off chance that they might be discovered and used in evidence against him.

The men now hunting him knew their way through the tunnels, probably with the aid of markings that fluoresced under infra-red light. They were going to take him through, too.

They were coming closer. He waited far up in the main gallery, in the mouth of a side tunnel. Now, behind p. 65 them, he could hear Dio's men. The noise of Caron's outfit stopped, then began again, softly.

Gray smiled, his sense of humor pleased. He tensed, waiting.

The rustle of cloth, the furtive creak of leather, the clink of metal equipment. Heavy breathing. Somebody whispered,

"Who the hell's that back there?"

"Must be men from the Project. We'd better hurry."

"We've got to find that damned Gray first," snapped the first voice grimly. "Caron'll burn us if we don't."

Gray counted six separate footsteps, trying to allow for the echoes. When he was sure the last man was by, he stepped out. The noise of Dio's hunt was growing—there must be a good many of them.

Covered by their own echoes, he stole up on the men ahead. His groping hand brushed gently against the clothing of the last man in the group. Gauging his distance swiftly, he went into action.

One hand fastened over the fellow's mouth. The other, holding a good-sized rock, struck down behind the ear. Gray eased the body down with scarcely a sound.

Their uniforms, he had noticed, were not too different from his prison garb. In a second he had stripped goggles, cap, and gun-belt from the body, and was striding after the others.

They moved like five eerie shadows now, in the queer light of the leader's lamp. Small fluorescent markings guided them. The last man grunted over his shoulder,

"What happened to you?"

"Stumbled," whispered Gray tersely, keeping his head down. A whisper is a good disguise for the voice. The other nodded.

"Don't straggle. No fun, getting lost in here."

The leader broke in. "We'll circle again. Be careful of that Project bunch—they'll be using ordinary light. And be quiet!"

They went, through connecting passages. The noise of Dio's party grew ominously loud. Abruptly, the leader swore.

"Caron or no Caron, he's gone. And we'd better go, too."

He turned off, down a different tunnel, and Gray heaved a sigh of relief, remembering the body he'd left in the open. For a time the noise of their pursuers grew remote. And then, suddenly, there was an echoing clamor of footsteps, and the glare of torches on the wall of a cross-passage ahead.

Voices came to Gray, distorted by the rock vaults.

"I'm sure I heard them, just then." It was Jill's voice.

"Yeah." That was Dio. "The trouble is, where?"

The footsteps halted. Then, "Let's try this passage. We don't want to get too far into this maze."

Caron's leader blasphemed softly and dodged into a side tunnel. The man next to Gray stumbled and cried out with pain as he struck the wall, and a shout rose behind them.

The leader broke into a run, twisting, turning, diving into the maze of smaller tunnels. The sounds