Galileo was watching all this so intently that he was shocked when a jarring halt to their descent smashed him into his chair.

“We’re down,” Hera said. “Come on.”

“Where to?” he said as he clambered up.

“Their power plant. That’s always the real seat of government.”

The grimness with which she said this gave Galileo the impression she had learned this truth in some personally disastrous way. But there was no time to inquire. She stuffed the pewter box of the tele-trasporta into a satchel-like compartment on the back of her space suit, and then they had the suits on and moved into the craft’s anteroom, putting on their space helmets, which reminded Galileo briefly of her memory celatone. Then they were out onto the blasted yellow of the Ionian mountainside.

OUTSIDE THE CRAFT, standing on the ground, Galileo looked around. Yellow sleet drifted down onto the slag a few miles away, splashing like rain when it struck. Out of this bizarre fountain shot twenty more sleek oval silver things, rocketing sideways with a dreamy speed. One of these craft tried to land right in the gap between two big low buildings of the settlement; a gate shut on it, and the craft buckled as it was caught. Hera shouted at the sight.

“Get their power off!” she snapped viciously, reminding Galileo of his mother. Uneasily he understood her as a general conducting a siege; no military officer he had ever met gave him the frisson of fear that he felt now as he regarded her. Imagine Giulia a general! The carnage would have been universal.

“Come on,” she snarled over her shoulder, and started running over the rugged plain toward the base. It had a kind of outer rock wall, it seemed, or was simply built on a broad low plateau. Galileo followed her toward it, struggling to keep up with her. She was big, and fleet of foot in a way he could not emulate, given the light pull of this moon, which caused him to launch up and forward with every stride, landing fearfully but again lightly, so that he could leap forward from one unsteady jaunt to the next, keeping his eye on Hera midleap, as it seemed to help his balance.

The slaggy plain of the volcano’s side was bigger than it looked. Silver craft still fell like stars out of the black sky. Behind them the towering yellow plume of the volcano rained down, plashing onto its previous spew. Figures in helmets, looking like white statues of the Swiss Guard, emerged from the gates of the city and pointed at them. Red afterimages suddenly crisscrossed Galileo’s vision, without him having seen anything to stimulate them in the first place. Hera stopped and held out a hand indicating he should stop too. In the general hissing silence, which was perhaps the rolling impact of the nearby plume striking him through his feet, he could not hear her voice. He could see that she was talking to him and that she thought he could hear her, but something must have gone wrong with his helmet, because there was no sound but the background hiss.

Abruptly she was off again. Galileo hurried after her, fearful of losing her and therefore his way.

They were approaching the village of silver buildings from an unexpected angle, it seemed, for the defenders were all focused on an attack from the other direction. Hera simply leaped forward onto two of these people, flying twenty or thirty feet before smashing into them like something thrown by a trebuchet. Down they went, while she bounced up and with a ferocious punch to the gut leveled another of them. Galileo followed her as fast as he could, but now she was really off, and no matter how hard he tried he could not keep up. He kept bounding off into space, and as he passed through a gate in a wall between two big buildings he crashed into an arch topping the gate, landing hard on his back and driving the wind out of him, and his guts out of his hernia too. He staggered back to his feet, stuck his fingers between his legs and shoved the truss up so that his guts would go back into his torso. After that he gave up on normal locomotion, instead making clumsy painful leaps forward, like a toad or a grasshopper, gasping all the while.

It was truly painful between his legs, but he was moving, and Hera was not far ahead of him when she finally came to a halt. He was mid-leap when he saw her stop and look to her left, and though he tried to twist in midair to dodge her, that of course didn’t work, and he bowled right into her back. It was like running into a wall, slightly padded; even as he was falling to the ground he was recalling the feel of the contact, the rocky substance of her ribs, the hard muscles of her bottom, with a layer of softness over the brick. Then he crashed down on his back and lay stunned at her heels, with his guts once again bulging out of his peritoneum. She had been knocked two or three steps forward by his impact, and in that moment a flash between them blasted him into a red blindness. Blinking through tears and the red bloom of bouncing afterimages, he saw her barking out orders without regard for him, as if he were her dog and had banged into the back of her knees while she was busy doing something.

By the time Galileo had shoved his guts back in and regained his feet, the local situation seemed to have come into compliance with her wishes. Defenders of the city lay twitching on a piazza they came to, looking like fish in the boxes at a market.

She grabbed him by the arm, and he indicated that he couldn’t hear what she was saying. She reached up and twisted at the outside of his helmet, under his right ear.

“Stand still,” she snapped.

“I’m trying!” he said. “At least I can hear you now.”

He shrugged free of her hold, which reminded him too much of his mother; the old witch had just such a clawlike grip. He swayed upright and held himself steady with a desperate effort of his whole body, glaring hotly at her. She was looking right back at him, both their faces behind clear faceplates that glowed with red numbers and diagrams in the corners, making it a literally red look that arced between them. Then the skin around her eyes crinkled; she was, for some reason, laughing at him.

“Your clumsiness saved my ass,” she said.

Galileo supposed she meant the flash that had blinded him. “I like your ass,” he said without thinking.

Her eyebrows rose. But she was still amused.

She returned to the business at hand. Her commands were still abrupt, but her tone was not so urgent. The situation was apparently in hand. The power station was occupied, she told him, the Gany-medean village therefore in their hands.

Then, listening to voices Galileo did not hear, her expression again blackened. She cursed and gave a quick series of orders under her breath.

“We didn’t shut them down fast enough,” she said grimly to Galileo. “Ganymede and his closest followers escaped. Six craft. Some of them are returning to attack us, presumably so that he can get clean away. We have to get back to the ship.”

“Lead on,” Galileo said.

Following her gamely back out of the city, he said, “Do you know where he’s going?”

“To Europa, I presume.”

“And who is attacking us now?”

“Some of his people. We have to get back to my ship as quick as we can.”

Outside the settlement, the black starry sky looked down on the scene, still eerily silent. The yellow plume to the east looked taller than a summer thunderhead. Even when an explosion flashed white and demolished one of the buildings behind them, there were no sounds, only a trembling underfoot. Galileo heard nothing but his own gasps, which seemed to come from outside his helmet, as if the cosmos itself were short of breath, and scared.

On the run back to her craft, the ground under his feet began to become sticky. It became like running on a viscous mud.

“Shit,” Hera said. “Apparently they set off some underground explosions just now. Big ones. One of my people say it’s the Swiss defense. The whole base will sink into the ground. A magma chamber has been breached, and it’s heating the ground in this area from below.”