“Turn yourself around. Nice slow movements, remember? Face the opening and once I start moving, just be ready to adjust our path if we veer toward one of the walls.”

“Just use my hands and feet?”

“Exactly. Nice slow movements. Keep repeating that to yourself.” The immune had struggled with keeping herself oriented in the lack of gravity on their first visit together, and Tania thought she had enough report with the woman now to offer some simple, if condescending, pointers.

A moment later, Vanessa had herself in position. Tania turned, again putting the hard, flat surface of her suit’s backpack against the case. She aimed her thruster toward Earth. The Elevator threads, all around her now, formed an ethereal tunnel that converged below in the haze and blur of clouds and atmosphere.

She turned, focused. A good five-second blast from the thruster and they were inside, moving at the equivalent to a brisk walking pace. The interior held a strange comfort to it now, on her third visit. Compared to the missing spikes outside, and the crowd of Elevator cords left in their place, the tunnel beyond the hexagon door looked exactly the same.

Stay sharp, she said to herself even as she added on another few seconds of thrust. She climbed around to the front of the case now, where Vanessa waited. Together they used their fingertips to push off the ceiling in a slight trajectory correction, and when the time came, they both put their legs and arms forward to take the brunt of the impact with the end of the hallway.

After a brief pause the wall at the end of the tunnel separated into angular sections, divided by bright lines of light. The lines grew into gaps as the sections of wall slid away to reveal the room beyond.

“We’re at the key room,” Tania said for Tim’s benefit.

“That was quick.”

“This place feels like a second home. Perhaps we should furnish it.”

Tim laughed. Vanessa did not. She’d flipped her gold sun visor up and Tania saw her eyes grow wide. “It’s changed,” the immune said.

Her tone ripped Tania’s attention from wrangling the object. She spun, and the room beyond sent a chill down her spine.

The ten-walled “key room” was gone. Instead she looked in upon a nearly spherical space, ten meters in diameter. Uncharacteristic for the Builders, the material was white, and it glowed with a faint luminance that seemed to come from everywhere and nowhere. The light, so dim it would have been hard to perceive had it not covered the entire interior, was alien in its flawlessness. A perfect, unwavering, evenly distributed light that constituted the white material’s only visible feature. Tania found herself wondering what it felt like. From appearance alone she could not tell if it was solid, or if her hand would pass straight through it.

Nestled within the glowing white sphere were two strips of metallic gray, each a meter wide and spanning the circumference of the room. The bands were perpendicular to each other, and met on the far side to form an X, exactly opposite where the door was.

Tim’s voice came through the speaker in her helmet. “Say something.”

“I’m not sure what to say,” Tania replied. “The key room is not here. We’re seeing a sphere. More in a second.”

She glanced at Vanessa and nodded once, a gesture the other woman returned. Tania pushed off gently and drifted toward the opening, wrapping one hand around the edge.

The gray material felt hard as steel through the glove of her suit. She moved her hand farther, then touched the white portion. To her surprise it had a spongy feel, like a firm cushion. Tania moved all the way inside and glanced around. Her first impression proved correct. Other than the two light gray bands, the room was completely featureless.

“What do we do?” Vanessa asked. She still floated in the hallway, next to the bagged object.

Tania continued across the space, then pushed off with her feet to drift back. She turned at the midway point to face Vanessa, and shrugged. “Bring it in, I guess. Let’s see what happens.”

Vanessa urged the bag forward and kept with it, matching the pace perfectly with slow, precise movements. Tania couldn’t help but smile at the immune’s progress. Soon she’d be bouncing about in zero-g like she’d lived in orbit for years.

Tania drifted out to meet them near the center of the room, not wanting to be near the wall if something happened. She’d barely moved a meter when the two bands began to move. They spun like wheels, independently of each other, and in doing so the opening they’d framed vanished. Tania’s breath caught in her throat. The rings, still spinning, began to tilt wildly, spinning on their axis now as well. Their motion revealed the portion of the sphere where the hallway had been just a second before. Tania saw nothing save for the pure, spongy white surface of the sphere where the only exit had been.

“Don’t panic,” she said, realizing a second later she’d said it aloud. “Tim, can you hear me?”

All she received in answer was a faint hissing sound from the speaker inside her helmet.

Vanessa tried. “Tim? Please respond.”

A few garbled words came through in bursts now.

“Some kind of interference,” Tania said.

Vanessa sucked in her lower lip in concentration. “Maybe this room is meant to sever our communication.”

Tania considered that. She wondered what would have happened had they come in here on some kind of umbilical or guywire. The motion of these two rings, she thought, would have severed it like a piece of string. The thought worried her.

The two metallic rings continued to rotate around the room, silent and ominous. Decelerating now, Tania thought. She studied them closely. “They’re slowing down.”

The two rings settled into a new position, forming X’s once again on opposite sides of the room. Different places than before, Tania thought, though she couldn’t be sure in the otherwise featureless bubble of glowing white.

The rings stopped rotating axially but still rolled along their own length. Tania watched, fascinated despite the sense of being trapped, as each ring began to slow to a stop. When they did, a new opening appeared where their surfaces met. In a perfect reversal of the exit hallway’s closure, panels slid apart on each band.

Tania felt the tension within her melt. The key room lay beyond. Only the entrance this time was in the middle of what she had considered the floor. She exhaled slowly as she took in the sight, looking for any other changes since last time, and saw none. Still the ten walls that rose a hundred meters above. Five were empty, just spacers really. Between each of those were the five that had receptacles for the objects, each wall alive with the color that matched its “key.”

“Didn’t we come in from the side last time?” Vanessa asked. “Why would they move the door?”

“A very good question.”

Through silent agreement, Tania pushed off to the new doorway and stopped herself at the opening. She took a quick stock just to be sure nothing here had changed.

“Come up here,” she said.

A moment later Vanessa joined her, the object still expertly placed in front of her for easy guidance. “What do you suppose that new room is for?”

Tania thought about it. “Some kind of junction, maybe? One that can reconfigure itself?”

The immune started to speak, stopped herself, then met Tania’s gaze. “I was going to ask why, or why now, but I’m not sure I want to know.”

“It would only be speculation,” Tania said. “I vote we call it the Lobby for now, and not worry about it. We’re here; let’s do what we came to do.”

Vanessa nodded. Together they turned and took in the alien majesty of the key room. Only the purple and red walls had exposed sections where their keys had been inserted. The objects themselves glowed with hues that matched their respective walls, only much brighter.

“There, look at the green,” Tania said, pointing.

Halfway up on the wall of emerald light patterns, a circle appeared as a section of the flat surface recessed into a half-dome cavity, just as before. Tania didn’t wait for the process to finish this time. Instead she set to work removing the wedge-shaped object from its case.

“This will be trickier than last time with these awful old thrusters,” Tania said.

“What can I do?” Vanessa asked.

Tania propelled the object in front of her with one hand and glided to the base of the green wall. Vanessa joined her a moment later, using Tania’s offered arm to stabilize and orient herself. They looked up in unison. The circular cavity was about fifty meters above, and hard to see from this vantage point.

On a whim Tania glanced back toward the room she’d dubbed the Lobby and saw no sign of it. No hint at all. Where a passage had existed moments before, she now saw only the perfect flat surface of the key room’s floor, and she found strangely enough that she felt completely at ease. It would open again, of this she felt absolutely sure. As alien as the ship may be, as any of the devices or places the Builders had sent, they all had a mechanical quality, a set of rules somewhere that governed how they worked. The idea carried a strange comfort she didn’t quite understand but also could not deny.

“You okay?” Vanessa asked. The immune had noted the lack of an exit, too, Tania saw. She nodded to her. “Just like last time, okay?”

“Okay.”

“Right, then.” With a slow, careful movement, she set the object in Vanessa’s hands. At the same instant a scramble of static came over her headset.

“Are you read— me?”

“Tim? Go ahead. You’re breaking up a bit.”

“Something’s coming up the —vator.”

“A climber, you mean?”

His response came through as a garbled mess. “Repeat,” she said, moving back toward the door. Memory of the spinning of Belem’s Elevator came to her. Once again she saw the mysterious dark “blobs” that had raced down that new cord, demolishing a supply climber as if it were a mere insect. Those shapes had become the aura towers, of which there were numerous examples directly below this ship, theoretically at least. Perhaps they were coming back? Her mouth went dry at the thought of forty of those dark masses hitting this ship with the same ferocity that single one had when it took out the climber.

Tim’s voice came through a bit clearer now. “I don’t——what it is, but it’s huge. The cords are lifting it.”

She tried and failed to imagine what “it” could be. What would they need to raise from the ground that required so much lifting power? There was simply nothing to relate such an action to, no analogue. She’d studied the early history of human space exploration, and the only thing she could think of was the soil return missions from Mars. Could this be the same, only on a scale that simply defied human imagination? “How quickly will it arrive?”

“It’s moving pretty slow. Faster than a climber, but not——. A few hours?”

“Okay,” Tania said. “Any change, you let us know. We’ll make sure to be out before it arrives, just in case.”

“Understood.”

Tania propelled herself back to Vanessa. “I guess we’d better hurry.”

“I’m ready.”

“Don’t forget,” Tania said. “Once we install it, there will be an energy buildup, and that bright flash. Remember? Okay. We’ll need to push off for here as soon as the object is inserted.” And hope the door reappears.

Vanessa signaled affirmative and got into position.

As per their plan, Tania pushed off from the floor and drifted along the wall. She had to force herself not to become mesmerized by the glowing green patterns along its surface. At the inside-out dome she stretched out her arm and, once on the far side of it, gripped the edge and stopped herself with ease. She turned and sat on the rim, mentally forcing herself to think of this as the new “floor.” “All set,” she said, and dug in the thick heels of her boots.

Vanessa pushed toward her, a clean and slow trajectory that was only a little off in aim. She was within arm’s reach by the time she reached Tania, and after a bit of awkward reorientation, the two women sat on either side of the cavity.

“Tim,” Tania said. “If you can hear us, we’re inserting the object now.” He made no response. Tania glanced at Vanessa. “On three, smooth, fluid movements okay? We push it into this bowl and it’ll take over. Then we push for the Lobby. I’ll guide you.”

At Vanessa’s nod Tania counted. At three she pressed her heavily gloved fingertips against the object, her eyes dancing between it and Vanessa to make sure they were in synch. As soon as the object broke the threshold of the cavity it began to glow more brightly. Then it started to turn, moved by an unseen force. It oriented so the corner with the missing tip pointed at the far end of the room. Tania gripped the edges of circular indentation and pulled her legs free of it, crouching on the green-patterned wall. Vanessa mirrored the action, moving a bit more confidently in the lack of gravity now.

Tania moved across the circular cavity, ignoring the mind-boggling display of materials science on display as the cavity began to reshape itself once again. She’d seen the process twice before and knew they had to move quickly, and yet she still found herself fighting the temptation to study the process. She gripped Vanessa by her forearm and felt the woman’s hand clasp around her own. Tania made eye contact with her. They knelt in unison and turned their bodies to face the “bottom” of the room where they’d entered.

“Visors down,” Tania said.

Vanessa swatted hers into position, leaving Tania looking at a gold-tinted reflection of herself. She flipped her own visor down an instant later, plunging her surroundings into near-total darkness. This did not last, though, as the extraordinary burst of light from the object they’d inserted continued to ramp up.