Tania forced the distraction away and willed herself to focus on the present, and on what little future she feared they had left. The oxygen gauge continued its slow, steady decline, hers faster than his. She needed to relax.

He raised his right arm and nodded at her to do the same. On a three-count that he timed to their arrival at the midway point along the wall, they both pulsed their thrusters to halt their momentum.

“I’m out of fuel,” Tania noted.

The concave recession on the purple wall was nearly pitch-black, just like the object they held. Skyler nodded to Tania again and used his own thruster, alone this time, to propel them the rest of the way to the wall.

“What now?” Tania said.

“I think we’re supposed to plug it in.”

He started to move to push the object into the cavity.

“Wait,” Tania said.

Skyler paused. He looked at her with one eyebrow raised.

She thought of what Neil Platz had written about her father. He destroyed it before we could truly learn. “We have no idea what this will do,” she said. “What if this is some kind of arming switch? A self-destruct mechanism? A trap?”

Skyler glanced at it, his brow furrowed, then back at her. “What if it bakes cookies?” When she frowned he tried again. “What if it activates an aura generator big enough for the entire planet? A ship of this size could do it.”

She opened her mouth, then closed it without answering. He was right. Faced with no knowledge, no context, there was no choice but to push forward into the unknown. If one trait defined humanity, surely it was that.

He took her silence as agreement and nudged the hourglass object into the inverted dome.

The hourglass began to glow as it crossed the threshold of the cavity. Faint at first, growing brighter with each centimeter. Then it rotated, pushed by some invisible force, and aligned itself with the room beyond. The edges of the inverted dome began to warp and reshape, taking on the same hourglass form and color. Soon the object and its receptacle glowed as bright as the wall around them. Then brighter, and brighter still.

On instinct, Tania pulsed back from the wall. Skyler followed her lead as the purple light grew to almost blinding intensity. Tania felt a vibration through her spacesuit, as if sound waves buffeted her despite the vacuum. The vibration grew in conjunction with the intense glow, and with it Tania noticed that the wave patterns within the purple glow along the wall became agitated, even violent. Her entire body began to shake, though whether from fear or some external pressure she couldn’t tell. “Skyler?!”

“I feel it!”

“What’s happening?”

With sudden, blinding ferocity the purple light exploded in a crescendo of energy that pushed her backward to the far wall. She smacked into the surface and felt her skull rattle against the inside of her helmet.

“Erg,” Skyler grunted.

Tania tasted blood, and realized she’d bit her tongue. For a moment she drifted, nothing but stars before her eyes and clouds in her mind. Her suit beeped and a mechanical voice said, “Concussion warning.” The alert repeated a few times.

Tania forced her eyes closed and held them tight until the residual energy patterns on her eyelids faded.

When she opened her eyes, she found herself at an odd angle, and a wave of disorientation swept over her. Light came from all around now. The purple wall pulsed and roiled, but there were new colors in the cavernous room. Five of the ten walls glowed now, giving the tall space a striped pattern of alternating light and dark. She saw red, green, and yellow, exactly like the other tower groups that had dispersed from Camp Exodus.

There was a fifth color as well, one not seen among the towers from Belém. Pale blue, as bright and pure as glacial ice under a clear summer sky.

She glanced up at the ceiling. The knobby hexagon in the center echoed all the colors from the walls around it simultaneously now. The reflections merged and danced hypnotically. One of the five ribs, the one that extended out to the edge and connected with the purple wall, now glowed with the same color.

“Unbelievable,” Skyler whispered.

“It’s incredible,” Tania agreed. She whispered, too, on pure instinct. She felt like a visitor to some ancient, forbidden temple.

A chime went off in Tania’s helmet. Skyler’s must have as well, because he glanced sharply at her. The air in her suit had reached 20 percent. Skyler’s readout showed just below 40.

“What now?” he asked.

“Nothing to do but wait,” she replied.

“I mean after we get rescued and get back home,” he said. He’d somehow forced a playful tone into his voice.

“I think it’s clear what we have to do next, though for what purpose I still cannot imagine.”

“At least we know where the red one is,” Skyler said. “The red … key.”

Tania studied him, a profound sense of dread building within her. He saw it in her eyes.

“Don’t worry,” he said. “We’ll go in with every weapon I can find, and some serious motivation.”

She tried to smile and couldn’t. Her gaze kept shooting back to the oxygen readout. “There’s five colors here, but only four tower groups left the camp. So where’s the fifth?”

“I can guess,” he said. “The one place an aura tower wouldn’t be needed.”

After a few seconds she understood. “Darwin.”

Skyler nodded, gravely.

“We need to talk to Russell Blackfield,” Tania said. The immune’s eyes narrowed to thin slits. “When I spoke with him after we fled to Belém, he gloated that our attempt to kill him from orbit failed. He also noted our failure at destroying Nightcliff, said we’d missed.”

“We didn’t drop anything on …” Skyler paused. Then, “Oh …”

“Exactly. Russell Blackfield can tell us exactly where the fifth ship crashed.”

Skyler frowned, but he was nodding all the same. A few seconds of silence passed, and their attention was drawn back to the light show within the vast room.

“We should wait by the exit,” Tania said quietly.

“I kinda like it in here,” he replied. “But you’re right. Hold on to me, I’ve still got some fuel left.”

He brought them to a stop just at the end of the hexagon tunnel. With nothing else to do, they floated side by side in the opening and watched the planet below as the line between day and night began to creep across the Sahara. The ERV was now a glinting speck in the distance. It would burn up in a few days, Skyler guessed, though Jenny had surely suffocated already.

She must have been one of Grillo’s, he realized. Or at least sympathetic to the Jacobites, if not one of them. Perhaps she’d been in contact with them during the flight and reported everything they’d found. He shuddered at the idea.

Skyler twisted to say something to Tania.

“Hold still,” she said.

She was working on something on the back of his suit. “What are you doing?”

“Just double-checking the air pack.”

He tried to keep from moving, a difficult trick without gravity.

“All set,” Tania said, and moved away.

He heard a slight quiver in her voice. A fear that hadn’t been there before. “We’re going to make it,” he said.

She didn’t reply. Instead she just looked at the planet below, and took his gloved hand in hers. For a long time neither of them spoke. Skyler kept thinking of things to say, only to find the silence somehow better.

A full half hour passed before his suit began to beep in warning. Hell. Not yet, surely? He fumbled through the menu to find his vitals readout, and saw that he had—

“That can’t be right.”

His oxygen level read almost 50 percent, higher than the last time he’d looked. Some kind of reserve tank they hadn’t known about, perhaps. He grinned. But why is it beeping at me?

It hit him, then. It wasn’t his suit complaining; it was Tania’s. In a panic he brought up the display of her vitals, and he froze when he saw the number. One percent. “Oh God, Tania, what did you do?”

She didn’t answer. Her hand had gone limp in his.

“Tania!” he shouted at her. He turned and took her faceplate in both hands. She was drifting in and out of consciousness, as if on the verge of sleep. “No, dammit!”

Her lips moved, but no words came through.

“Why?!” he shouted again, fighting tears. The answer, he realized, was obvious.

The speaker in his helmet crackled then. A voice within a harsh cascade of static. “… is … condition? Repeat …”

“Get the fuck over here, now!” Skyler blurted, aware of how shaky he sounded. “She gave me her air. She’s almost out!”

“… Approaching … ETA in … minutes.”

Skyler put his helmet against hers, looking for any sign of life. He held his own breath and waited. Seconds passed. He thought he saw a puff of condensation on the inside of the helmet. A breath. “You hold on, dammit. Hold on, they’re close.”

Another puff against the glass, weaker than the last.

Then another.

And then nothing.