Scholes pushed the lock closed, and Larionova was plunged into sudden darkness.

Scholes loomed before her. He was a shape cut out of blackness. "Are you okay? Your pulse is rapid."

She could hear the rattle of her own breath, loud and immediate. "Just a little disoriented."

"We've got all of a third of a gee down here, you know. You'll get used to it. Let your eyes dark-adapt. We don't have to hurry this."

She looked up.

In her peripheral vision, the stars were already coming out. She looked for a bright double star, blue and white. There it was: Earth, with Luna.

And now, with a slow grandeur, the landscape revealed itself to her adjusting eyes. The plain from which the rover had climbed spread out from the foot of the crater wall-mountain. It was a complex patchwork of crowding craters, ridges and scarps -- some of which must have been miles high -- all revealed as a glimmering tracery in the starlight. The face of the planet seemed wrinkled, she thought, as if shrunk with age.

"These wall-mountains are over a mile high," Scholes said. "Up here, the surface is firm enough to walk on; the regolith dust layer is only a couple of inches thick. But down on the plain the dust can be ten or fifteen yards deep. Hence the big wheels on the rover. I guess that's what five billion years of thousand-degree temperature range does for a landscape..."

Just twenty-four hours ago, she reflected, Larionova had been stuck in a boardroom in New York, buried in one of Superet's endless funding battles. And now this... wormhole travel was bewildering. "Lethe's waters," she said. "It's so -- desolate."

Scholes gave an ironic bow. "Welcome to Mercury," he said.

Cilia-of-Gold and Strong-Flukes peered down into the Chimney cavern.

Cilia-of-Gold had chosen the cavern well. The Chimney here was a fine young vent, a glowing crater much wider than their old, dying home. The water above the Chimney was turbulent, and richly cloudy; the cavern itself was wide and smooth-walled. Cilia-plants grew in mats around the Chimney's base. Cutters browsed in turn on the cilia-plants, great chains of them, their tough little arms slicing steadily through the plants. Sliding through the plant mats Cilia-of-Gold could make out the supple form of a Crawler, its mindless, tubelike body wider than Cilia-of-Gold's and more than three times as long...

And, stalking around their little forest, here came the Heads themselves, the rulers of the cavern. Cilia-of-Gold counted four, five, six of the Heads, and no doubt there were many more in the dark recesses of the cavern.

One Head -- close to the tunnel mouth -- swiveled its huge, swollen helmet-skull towards her.

She ducked back into the tunnel, aware that all her cilia were quivering.

Strong-Flukes drifted to the tunnel floor, landing in a little cloud of food particles. "Heads," she said, her voice soft with despair. "We can't fight Heads."

The Heads' huge helmet-skulls were sensitive to heat -- fantastically so, enabling the Heads to track and kill with almost perfect accuracy. Heads were deadly opponents, Cilia-of-Gold reflected. But the people had nowhere else to go.