Now, most of the power had been cut off, as Isak had ordered, and all the fields were withering in the night. The pioneering days were over. From now on, the Cerans would draw their nourishment using the old standby methods of deep space explorers living in cramped and energy-efficient quarters. After the last crops were harvested, and the last of the cattle killed, each family would be reduced to a meter-square box of lights and tubes filled with recombinant algae. From these gardens of algae would come all the food ever to be produced again inside Ceres. There was simply no energy for anything else.

“Fission reactors,” Isak said at last. “How long will the fuel last?”

“Thorium won’t last indefinitely, sir. We’ll have to think of something else as soon as we can.”

Isak’s pad chimed and flashed red, throwing up a star chart with Earth at its center as the computer said, “Those two nearer gamma ray sources are growing stronger. I have identified them as our Valkyrie starships, Nautile and Graff, decelerating from Barnard’s Star. They are down to sunspace cruising speed—one hour, fifty-seven light-minutes away. They continue to call for information on all channels, from anyone who can hear them. Instructions?”

“Maintain silence,” Isak said. “Do not answer under any circumstances.”

Stealthily, Isak and Sargenti—and every other inhabitant of Ceres—watched as the two Valkyrie ultralight starships fell homeward, broadcasting every kilometer of the way. Then the pilot of Graff started to speak in German, words of astonishment, and his gamma flare died in the middle of course correction. The Nautile quit without any words at all.

Isak guessed that only the German had lived long enough to see something, and it had stupefied him. He had let out two or three exclamations before trying to describe it, and by then, of course, he couldn’t.

Now, two dwarf novae burned where the Valkyries had been, emitting gamma flares and plasma shock bubbles that in certain wavelengths lit up their small corner of the heavens fiercely enough to drive back the glow of Sagittarius. The expanding concussion of light brought home to everyone the message of the destroyed Valkyries: it was fatal to communicate. Something ruthless and fast acting had entered the solar system, and whatever it was, it was looking for them.

“No surviving human group,” Isak said, pushing his chair back from the table, “can choose not to power down.”

Sargenti was taking in the lesson of the fading novae on the pads. Her usually pale face was flushed. Her tall, willowy frame was hunched down over Isak’s table, and she was breathing fitfully.

Isak turned away from her and looked out across the fading light of his amaryllis garden, while on the twin pads the plasma dissipated and Sagittarius returned to prominence again.

Sargenti watched the cold stars burn, wondering if somewhere out there the Intruders knew her thoughts, could actually trace them like streams of neutrinos to their source and read them, if such could conceivably be the extent of alien power. No. Isak would say that this was worrying about another cracked heat shield, she realized—and tried to shrug the idea away. Neutrino glow you could reduce and hide, radio waves you could hide. How, she asked herself, does one go about hiding one’s thoughts?