And the eerie sounds in his earphones had stopped, too.

I've overshot him, Doug told himself. He's back behind me someplace. Down inside the rille. Hiding.

Slowly, bending over the edge of the rille to examine its bottom, Doug started backtracking. He couldn't see the bottom of the arroyo, it was too deep for his helmet lamp to reach.

He stopped and listened. Nothing. Gordette had gone silent. Is he dead? Maybe what I heard was his last gasping for air.

With great reluctance, and more than a little fear, Doug carefully climbed down inside the rille, lowering himself slowly down as far as he could with his arms fully stretched, then letting himself slide the rest of the way down.

He felt the rough side wall grating against the chest of his suit. Couldn't do this in a fabric suit, he thought. The cermet won't tear. But he knew that grinding some dust or larger particles of grit into his suit's joints could immobilize him as thoroughly as the Tin Woodsman caught in a monsoon rain.

Doug had never felt the panic of claustrophobia, but as he stood shakily inside the narrow rille he saw that the sky above him was nothing more now than a constricted slice of stars cut off on both sides by the steep black walls of the arroyo. Like the view from the bottom of a grave, he thought.

He took a step forward and his boot slid on the glass-smooth rock. He had to grab at both sides of the gully to keep himself from falling. Hardly any dust down here, he realized. This rille must be brand-new, maybe still active.

"New' and 'active' were relative terms on the Moon, he knew. A new rille might have opened up only a few thousand years ago. Its activity might be a slight sigh of underground gas every century or so.

A cough. In his earphones Doug heard somebody cough. Couldn't be anybody but Bam.

Slowly, moving cautiously along the slippery rock floor of the rille, both hands extended to touch its steep confining walls, Doug made his way forward.

Another cough, followed by a quick, desperate gasping.

"Bam!" he called into his helmet mike. "Bam, where are you?"

No response. Standing stock-still, Doug listened hard. Is he holding his breath? No, it's just so faint I can hardly hear him.

Doug pushed along the slick arroyo and the sound of Gordette's breathing grew louder. It sounded strained, labored, as if the man were in pain.

"I'm coming, Bam," Doug called again. "I'll be with you in a couple of minutes. Hang on."

"Don't…' Gordette's voice was weak. It broke into a gasping cough.

"Save your breath. I'll be there."

"Careful… the ground… gives way…"

Doug scanned the ground before him in the light of his helmet lamp. It looked solid enough, glassy and slick, but solid rock. Yet he knew this volcanic vent might be no sturdier than a soap bubble.