He looked up at Larionova, his moonlike face animated. "Irina. They've found another mercuric," he said.

"Is it intact?"

"More than that." Dixon stood and reached for his helmet. "This one isn't dead yet..."

The mercuric lay on Chao's dust-coated ice. Humans stood around it, suited, their face plates anonymously blank.

The mercuric, dying, was a cone of bruised-purple meat a yard long. Shards of shattered transparent carapace had been crushed into its crystallizing flesh. Some of the cilia, within the carapace, stretched and twitched. The cilia looked differently colored to Dixon's reconstruction, as far as Larionova could remember: these were yellowish threads, almost golden.

Dixon spoke quickly to his team, then joined Larionova and Scholes. "We couldn't have saved it. It was in distress as soon as our core broke through into its tunnel. I guess it couldn't take the pressure and temperature differentials. Its internal organs seem to be massively disrupted..."

"Just think." Kevan Scholes stood beside Dixon, his hands clasped behind his back. "There must be millions of these animals in the ice under our feet, embedded in their pointless little chambers. Surely none of them could dig more than a hundred yards or so up from the liquid layer."

Larionova switched their voices out of her consciousness. She knelt down, on the ice; under her knees she could feel the criss-cross heating elements in her suit's fabric.

She peered into the dulling sonar-eyes of the mercuric. The creature's mandibles -- prominent and sharp -- opened and closed, in vacuum silence.

She felt an impulse to reach out her gloved hand to the battered flank of the creature: to touch this animal, this person, whose species had, perhaps, traveled across light years -- and five billion years -- to reach her...

But still, she had the nagging feeling that something was wrong with Scholes' neat hypothesis. The mercuric's physical design seemed crude. Could this really have been a starfaring species? The builders of the ship in Caloris must have had some form of major tool-wielding capability. And Dixon's earlier study had shown that the creature had no trace of any limbs, even vestigially...

Vestigial limbs, she remembered. Lethe.

Abruptly her perception of this animal -- and its host parasite -- began to shift; she could feel a paradigm dissolving inside her, melting like a Mercury snowflake in the Sun.

"Dr. Larionova? Are you all right?"

Larionova looked up at Scholes. "Kevan, I called you a romantic. But I think you were almost correct, after all. But not quite. Remember we've suggested that the parasite -- the infestation -- changes the mercuric's behavior, causing it to make its climb."

"What are you saying?"

Suddenly, Larionova saw it all. "I don't believe this mercuric is descended from the starfarers -- the builders of the ship in Caloris. I think the rise of the mercurics' intelligence was a later development; the mercurics grew to consciousness here, on Mercury. I do think the mercurics are descended from something that came to Mercury on that ship, though. A pet, or a food animal -- Lethe, even some equivalent of a stomach bacteria. Five billion years is time enough for anything. And, given the competition for space near the short-lived vents, there's plenty of encouragement for the development of intelligence, down inside this frozen sea."