Madeleine frowned. “Lena, did Ben encourage you to show me this? Are you trying to persuade me to back off the Nereid project?”

“Ben and I have different experiences,” Lena said. “He traveled to the stars, and saw many things. I worked here, helping to uncover this strange, ancient tragedy.”

Yes. There was no need to go to the stars, Madeleine saw now. It was here, all the time, on Venus and Triton and God-knows-where, and even Earth. The central paradoxical mystery of the universe. Everywhere, life emergent. Everywhere, life crushed. And no explanation why it had to be this way. Over and over.

She felt her anger burn brighter. She had made her own decision. This wasn’t simply what Nemoto wanted. It had become what she wanted. And that burning desire felt good.

Lena smiled, gnomic, wise.

By the time they got back to Kasyapa, the flower-ships had grown in Triton’s sky, until at last their delicate filigree structure was visible, just, with the naked eye. The same fucking Gaijin who had watched as Earth had gone to hell.

She sailed up to orbit, boarded Gurrutu, and headed for Nereid.

Madeleine first sighted Nereid ten days out. It grew rapidly, day by day, finally hour by hour, until its battered gray hide filled the viewing windows.

Rendezvous with the hurtling rock was difficult. The Gurrutu couldn’t muster the velocity change required to match Nereid’s crashing orbit. So Madeleine had to burn her engines and use tethers, harpooning this great rock whale as it hurtled past, letting her ship be dragged along with it. Gurrutu suffered considerable damage, but nothing significant enough to make Madeleine abort.

She entered a loose, slow orbit, inspecting the moon’s surface. Nereid was uninteresting: just a misshapen ball of dirty ice, pocked by craters; it was so small it had never melted, never differentiated into layers of rock and ice like Triton, never had any genuine geology. Nereid was a relic of the past, a ruin of the more orderly moon system that had been wrecked when Triton was captured.

But, despite its small size, it massed as much as 5 percent of Triton’s own bulk. And where Triton’s orbit, though retrograde, was neatly circular, Nereid followed a wide, swooping ellipse, taking almost an Earth year to complete a single one of its “months” around Neptune.

Nereid could be driven head-on into Triton. It would be a useful bullet.

She navigated with automatic star trackers, with radio Doppler fixes on Kasyapa, and by eye, using a sextant. Her purpose was to check the trajectory of the little moon, backing up the automated systems with this on-the-spot eyeballing, which, even now, was one of the most precise navigation systems known.

Nereid was right on the button. But this game of interplanetary pool was played on a gigantic table, and Triton was a small target. Even now, even so close, Nereid could be deflected from its impact.

At times the cold magnitude of the project — sending one world to impact another — awed her. This is too big for us. This is a project for the arrogant ones: the Gaijin, the others who strangled Venus and Triton.

But when she was close enough, she could see the glow of engines on Nereid’s far side: engines built by humans, placed by humans. Placed by her. She clung to her anger, seeking confidence.

Even now Ben debated the ethics of the situation with his people. Most people here had been born long after the emigration: born in the caverns of Kasyapa, now with children of their own. To them, Madeleine and Ben Roach were intruders from the muddy pool at the heart of the Solar System, invaders from another time who proposed to smash their world. The shortness of human lives, she thought. Our curse. Every generation thinks it is immortal, that it has been born into a world that has never changed, and will never change.

She dozed in her sleeping compartment, a box little larger than she was. Inside, however, tucked into her sleeping bag with the folding door drawn to, she felt comfortable and secure. She would track Nereid as long as she could, guiding it to its destination, unless she was ordered to stand down.

She got a number of direct calls from Nemoto that she did not accept. Nemoto was irrelevant now.

At the very last minute Ben came through.

Somewhat to her surprise, the colonists had agreed to let the project go ahead. Ben would arrange for the temporary evacuation of the colonists from Kasyapa, to the hulks of the old transport ships still in orbit, now drifting without their engines.

“Lena is pleased,” he told her.

“Pleased?”

“By your reaction to the crystal shell around the core. The ice eight. She wanted to make you angry. If the project succeeds then the crystal shell will be destroyed. And the last trace of the native life will surely be destroyed with it.”

Madeleine growled. “I know, Ben. I always knew. The Triton bugs lost their war a long time ago, before they even had a chance to voice an opinion. Their memory should motivate us, not stop us. The crystal builders have gone, but the Gaijin are on their way, here, now. Well, the hell with them. This is the trench we’ve dug, and we aren’t going to quit it.”

“If,” he said, “the Gaijin are the true enemy.”

“They will do for now.”

He smiled sadly. “You sound like Nemoto.”

“None of us age gracefully. Why didn’t you tell me about the native life, Ben?”

His virtual image shrugged. “Not everybody who’s grown up here knows about it. Life is hard enough here without people learning that there is an alien artifact of unknown antiquity buried at the heart of the world.”

She nodded. And yet he hadn’t answered her question. Despite all we’ve been through — even though we’re both refugees from another age, and we traveled to the stars together — I’m not close enough for you to share your secrets.

At that moment, she felt the ties between them stretch, break. Now, she thought, I am truly alone; I have lost my only companion from the past. It was surprising how little it hurt.

“Here is another possibility,” Ben said. “Beyond ethics, beyond this perceived conflict with the Gaijin. You like to meddle, to smash things, Madeleine. You are like Nereid yourself, a rogue body, come to smash our little community. Perhaps this is why the plan is so appealing to you.”

“Perhaps it is,” she said, irritated. “You’ll have to judge my psychology for yourself.”

And with an angry stab, she shut down the comms link.

Alone in Gurrutu, she assembled a complete virtual projection of Triton, a three-dimensional globe a meter across. She looked for the last time at the ice surface of Triton, the subtle shadings of pink and white and brown.

She switched to a viewpoint at Triton’s evacuated equator. It was as if she were standing on Triton’s surface.

Nereid was supposed to do two things: to spin up Triton, and to melt its ancient oceans. Therefore she had steered the moon to come in at a steep angle, to deliver a sideways slap along Triton’s equator. And so, when she turned her virtual head, Nereid was looming low on the horizon: a lumpy, battered moon, visibly three-dimensional, rotating, growing minute by minute.

An icon in the corner of her view recorded a steady countdown. She deleted it. She’d always hated countdowns.

Her imaging systems picked out Gaijin flower-ships in low orbit around the moon, golden sparks arcing this way and that. She smiled. So the Gaijin were curious too. Let them watch. It would be, after all, the greatest impact in the Solar System since the end of the primordial bombardment.

Quite a show. And for once it would be humans lighting up the sky.

The end, when it came, seemed brutally fast. Nereid grew from a spot of darkness, to a pebble, to a patch of rock the size of her hand, to, Jesus, a roof of rock over the world, and then—