She lay back on the viewing bench, drained but elated. “Half done,” she muttered. Now all she had to do was measure the effect when the light from the same star took the longest possible path through her own world’s atmosphere—and then she’d finally know whether the most dangerous moment in her life was one she’d already lived through, or whether there was greater danger still to come.
“I’ll race you to the next level,” Joanna said, tensing her body in preparation to start bounding up the stairs.
Rosalind groaned. “Not today. If you’re bored, feel free to run ahead of me, but I just want to conserve my strength.”
“But we’re almost there!” Joanna remained beside her, keeping step with Rosalind’s measured ascent, but she was fidgeting impatiently as she spoke. “The sooner we arrive, the more daylight will be left.”
Rosalind didn’t reply; she had no intention of increasing her pace. Before a jump, she needed to be calm and unhurried. If she sprinted up the stairs, she might gain the advantage of a little more time before nightfall, but it would come at the cost of finding herself standing on the ledge feeling as if she’d been chased there.
The sun had just come out from behind Tvíburi, and it was still so high that its light had to travel obliquely through the wall of ice around them, bringing a diffuse, bluish glow to the western half of the spiral staircase. As she emerged from the shadow of the central column into the soft blue light, Rosalind contemplated the roots embedded in the ice, most visible as backlit silhouettes, but breaking through the wall in places to sprout the flowers that kept the air replenished. The Yggdrasil had served them well, but they had deceived it horribly. If she’d been alive at the time the tower was begun, she would have bet anyone that the tree would get wise and stop cooperating, long before its roots had accreted a spike of ice stretching halfway to Tvíburi.
“Can you imagine never having to climb stairs again?” Joanna asked. She made the prospect sound surreal.
“You don’t think we’ll be raising a tower of our own?” Rosalind teased her.
“Someone else can do that job.”
“Really? Who exactly are you volunteering?”
Joanna said, “The children. I’ll farm the crops, they can farm the ice.”
“Why not?” They all had their own peculiar fantasies as to how the new life would be—and there was no point cautioning anyone not to get ahead of themselves. However solid its foundations, the tower itself had only kept rising through the sheer force of its creators’ endlessly malleable hopes.
By mid-afternoon, a section of the wall had grown so bright that Rosalind was left half-blinded by its lingering afterimage each time she walked into the column’s shadow. The stairs were meant to be uniform, and she ought to have been able to climb them with her eyes closed by now, but though she knew roughly where the dozen or so mistakes were in every flight, she didn’t have the kind of flawless memory that would allow her to anticipate exactly when her ascending foot would need to land a little higher, or lower, or farther ahead. In any case, the occasional risk of a mis-step did nothing to make the journey less monotonous. The best thing about this trip was that she wouldn’t be taking the stairs back down.
“You have to promise that you won’t follow me,” she told Joanna sternly.
“I don’t even have my glider!” Joanna protested. “I’m just here for moral support.”
“I wouldn’t put it past you to have something hidden up there.”
“Only food,” Joanna replied. “But who doesn’t keep a few seeds stashed on every level?”
“What kind?” Rosalind wondered. She hadn’t eaten at all when they’d rested at noon.
“None of your business! You’re meant to be flying light!”
“A handful of seeds won’t kill me.”
“I vomited in midair once,” Joanna confessed. “It might not have been fatal, but it was certainly distracting. So don’t expect any last minute snacks from me.”
Rosalind started laughing.
“What’s so funny?” Joanna demanded.
“I’ve vomited a lot more than once.” How was it that nobody knew that the team’s most experienced flier had heaved up the contents of her stomach—however meager it was—at least as often as she’d managed to keep it down?
“At last!” Joanna pressed her hand gratefully against the sign on the wall promising the end of level thirty-six, then raced ahead and disappeared around the curve of the staircase. Rosalind felt a twinge of impatience herself, but maintained her pace; if she was going to break a leg today, she’d rather save that for a more appropriate moment.
As she stepped onto the landing, she saw Joanna waiting by the exit. “You don’t have to come out with me,” she said.
Joanna scowled. “I didn’t climb all this way to stay inside.”
Rosalind hesitated. “What happened to your stash? Have you eaten it already?”
“No, it’s…” Joanna gestured toward the connecting chambers for level thirty-seven; the pressure difference wasn’t much, but it would still take time to go through and back. “I’ll wait until you’re done here.”
“All right.” Rosalind walked over to the exit and opened the first door; when she closed it behind her she was in total darkness. She squatted down and started checking the seal, probing it with her finger from bottom to top. A speck of grit had become caught in the strip, so she opened the door again and brushed it away, then repeated the procedure.
There were six doors in total. The seals were good, but they couldn’t be perfect, and in combination they probably ended up leaking air at about the rate the root flowers were replenishing it.
Rosalind emerged from the darkness of the final chamber into dazzling sunshine. It was late afternoon, but out on the balcony the light was much stronger than down on the ground. Her skin tingled oddly in the rarefied air, and she could feel the rigid muscles closing off her windpipe, more efficiently than any of the door seals. She’d taken her last breath for a while.
She put her pack on the floor and slid the panels out, then set to work assembling her glider. Every individual panel had probably been replaced four or five times, and the bracing rods and runners even more often, but she still thought of it as the same one she’d used for her first serious jump.
Joanna stepped through the door, squinting at the sunlight. They nodded to each other, then Joanna approached and clasped her friend’s shoulder. Rosalind squeezed her hand reassuringly: this had to be done, and it would be over soon enough. But it was a cruel irony that the cost of being here meant that Joanna would be the last to know the outcome, when all their other friends were already waiting at the base of the tower to greet the returning flier.
Rosalind finished putting the glider together, then spent twice as long checking it. One of the rods felt stiff; she pulled it out and replaced it with a spare. After that, when she pushed against the frame it responded like a single object, precisely as supple and as strong as she needed it to be.
She propped the glider up against the wall of the tower, turned her back to it, and strapped herself in, securing the belt around her waist.
All this time, she’d been so far from the edge of the balcony that the ground had remained out of sight. As she walked forward, the horizon took longer than she expected to appear: it was even farther below her eye-line than the last time. She was afraid to look up at Tvíburi, to compare the angles the two worlds subtended, as if that might drive the point home far more ruthlessly. She was still a long way from the top of the tower, but some kind of dream-logic tugged at her mind, whispering that if she wasn’t careful, she might end up falling toward the wrong world.