The buzz of people hurrying home for supper was just audible at this height. She didn't mind waiting for Check to finish pruning because it meant she got to witness the best spectacle the city had to offer as the hundreds of thousands of windows began to glow softly as dusk settled over the city.

She grabbed onto an ivy branch to swing around and watch her brother carefully snipping leaves from the blighted area.

"Let's go, Mr. Rot Expert. The tree lights are coming on." Marina pointed at the bioluminescent trees that lined the street below which were becoming brighter moment by moment. "We're not supposed to be up here past sundown."

"You don't need to remind me," Check said, snipping a last bunch of ivy from the wall and reaching over his shoulder to tuck it into the large pack strapped to his back.

"It seems I do, since every day you'd be up here way past sundown, which means I'd be up here way past sundown, which means we'd both get written up for unsafe maintenance."

She crossed her arms in mock-anger over her chest, which allowed the wind to swing her out over the void between the buildings again. She bumped gently back into the ivy-covered wall and continued glaring at her brother, who hung several feet away in his own harness, frowning at the wall as he examined another strand of ivy before clipping it.

"Come on!" she insisted.

"Alright, alright. Galna is waiting for me anyway." Check pushed the handful of ivy into his bulging bag and began pulling on the hemp cord to hoist himself back to the building's roof.

"Isn't she always?" Marina muttered. As they ascended, she didn't let up. "Why are you so intent on working so much overtime, big bro? How many credits does one person need, anyway? You've been out here from sun-up to sundown every day for months. You must have hundreds of credits compiled by now. You don't even spend them - Oh! Ohhhh..."

At the long drawn out syllable Check stopped, about to hoist himself up, one hand on the edge of the roof and his booted toe wedged into the decorative line that ran around the edge of the roof, but was really for the purpose of the workers who went up and down the outside of the building maintaining the plant covering that spread over different floors.

His eyes narrowed as he watched Marina pull herself up over the edge of the roof and begin coiling up her ropes. "What was that 'oooohhhh' and what is that smile for?"

With the practice of a sibling, she ignored her brother's stare and refused to make eye contact, instead taking her time examining the lengths of rope that she pulled up before wrapping them expertly around her hand and arm and binding them with the harness.

She nonchalantly remarked, "I need to stop by the Hemp House to get a new section of rope. If you need any, I can add it onto the maintenance hours I do for them. Where are you headed now?"

"I do need another six feet myself, actually. I'm stopping by the chemist's then going to Galna's." Check attached his ropes to his pack and slung the whole thing on his back before absently pushing through the topiary to reach the rooftop door.

"Chemist's, huh? Something you and Galna need from there?" Marina barely contained a giggle then said more loudly, "I'm almost out of my shampoo bar and I need to settle my account with them. Frantin covers their building, so we've got to discuss where else I can do the work to pay it. Hey, I haven't seen Galna in forever. I'll come with you to say hi."

Check stopped with a foot on the top step. "The last time you came to Galna's you said your head was going to explode from boredom."

"All you two do is look through microscopes. That is boring."

He chuckled. "To each their own. Isn't there a match on tonight you're hot and heavy to bet on?"

Marina gave him a little shove. "Get walking, Check. Your pack takes up the whole stairwell. The match isn't until midnight. The earlier one got cancelled because Denit got hurt repairing the aviary."

"No! What happened? Is he alright?"

Marina shoved again and followed her brother down as she explained. "The bolts made of that new alloy the Academy green-lighted gave way when he was walking over the top beam to get to the central panel. Whole thing crashed down. It got caught in the safety net, but a few birds got clipped too from smaller pieces of glass that fell through. Denit got a few bad cuts. Not enough to put him off work, but enough to take him out of the wrestling pit until he's healed up. If there's a last minute replacement I'll get a notification and head over."

"Isn't that the same alloy you got in trouble over?"

"Let's not talk about it," she replied and stabbed the lift button.

They waited for the aqualift in companionable silence and rode it to ground level.

Marina looked up at the rooftops where they'd just been. The delicate green light of the bioluminescent trees just reached the third floors of the buildings above them. Beyond that only alternating darker stripes of floors covered in greenery and those without were visible against the darkening sky. Within an hour, even that would barely be discernible and only strips of the starry sky, filled with innumerable stars, would delineate where the tops of the buildings were.

Half an hour later Marina followed Check up the steps of Galna's house. She didn't remark on the fact that he opened the door with his own key and led her in without ringing the bell, or how he kicked his shoes off at the door next to Galna's.

"Where's Galna?" Marina asked.

"She'll be in the lab out back. I'll get her and meet you in the kitchen."

With his pack still on, Check headed down the hallway lit by a bioluminescent vine, returning minutes later sans pack and with Galna in tow.

Her brother's long-time friend launched herself forward, making her springy black curls bounce. "Marina! It's been so long since I've seen you! How have you been? How's your betting kingdom - or I should say 'queendom' - going?"

Marina returned the hug warmly and asked incredulously, "You've heard of that?"

"One of the organisers asked me to verify that it was possible to bet like you do and win without the matches being rigged."

"They seriously think I'd do that?" Marina responded, affront evident in her voice.

Galna shook her head. "No, they don't. They had to check just to quiet the people who think you would. I told them the truth."

"Which is?" Marina prompted when Galna didn't elaborate.

"That you're a brilliant mathematician with a nose for winners. Luck meets intelligence. Speaking of which-"

Marina watched as Galna turned to Check who looked up from taking a casserole from the baking bag and shook his head. They had a silent, but furious, conversation comprised of raised eyebrows, head shakes and shoulder gestures that had Galna huffing in frustration at the end.

"What was that all about?" Marina inquired, pulling out one of the leaf-shaped chairs from the bamboo table and sitting down. "A lover's quarrel?"

"A what?" sputtered Check and glanced at Galna whose face was rapidly pinking up. "We're not-"

"There isn't anything going on," insisted Galna. "We're just work mates. Partners. Friends. We're friends. Who work together. Work friends. That's all." She laughed nervously and set down a stack of plates on the table with a clatter.

Marina leaned back on her chair. "Then what was that little argument about."

Check crossed his arms over his chest and glared. "Galna wants to ask you to look over something, and I don't think we need to."

"And this something is?"

"Check, come on. You know she's the best mathematician in the city, even if the Academy won't forgive her and let her back in. More than that, you trust her. She won't tell." Galna stepped closer to Check and looked up into his face.

Marina smiled inwardly as she watched her big beefy brother's face soften and his resolve to uphold his argument crumble before the pleading look Galna was giving him. Just like an old married couple madly in love.

"Before or after we eat?" Check relented.

A smile bloomed on Galna's face that rivalled the beauty of the intricately decorated walls. "During. I'll get the notebook. It's all we need to start."

Moments later they dug into Galna's spinach casserole.

"Mmmm," Marina moaned. "When I get my own house, I want you to grow my spinach for me. Yours always tastes the best."

"Your kidding me, right? You're brother does all my wall-plant maintenance for me. It's his green thumbs that have made my house bloom like it does."

"Is that so?" Marina said dryly and pulled over the bamboo-spiral notebook Check had put on the table.

Check gave her an apologetic shrug. Marina had asked him for help on numerous occasions with the plants on the outside of her apartment, but he always said he was too busy or he didn't want to garden after doing it all day at work. She cocked an eyebrow and looked meaningfully between him and Galna. Check glanced at the woman portioning the lasagna and nervously rolled his shoulders.

Marina shook her head and flipped open the book. She turned her attention to the equations, eventually shovelling food into her mouth out of habit as the math captured her. When she started muttering about mistakes, Galna pressed a slim bamboo pencil into her hand so she could make corrections.

"Where is the experiment?" Marina asked, finally closing the book.

"What?" Check and Galna asked in unison.

"I recognize most of the ingredients you're putting together, and how. You were close, but I bet it wouldn't gel, would it? This ingredient here. What is it? It's what's causing the problem." Marina looked expectantly between them.

Check and Galna turned to each other with eyes wide.

"You can tell all that from my notes? How can the Academy keep you out?" Check asked.

"They didn't like my criticisms ... and maybe blowing up that last experiment wasn't the best way to get my point across." Marina shrugged. "After Denit's accident, maybe they'll listen. Everything I predicted about that alloy is starting to happen. So, where is your experiment?"

After another silent conversation of Galna's drawn brows and Check's face going from pleading to nervousness, they silently followed the path of the bioluminescent tree's roots along the walls deeper into the house. Galna's family had been training them for a couple of generations to travel along the walls from the tree's trunk that formed a central pillar in the middle of the house.

They entered a large room made small by several bioluminscent trees that lit the back room brightly, chalkboards full of equations covering one wall, and workbenches with different laboratory paraphanelia scattered throughout.

It was the large illuminated tank in the centre that drew Marina directly to it. Now she knew the ingredient she couldn't identify in the equations.

"Where did you get these?" she gasped, watching the small jellyfish bobbing around in the water.

"This is where all of my extra credits go."

"Big bro, I would have fronted whatever you needed. You just need to ask."

Check shook his head. "If this doesn't turn out, I don't want anyone to go down with me. You remember how Grandfather was ostracised and ridiculed for his theories on harvesting jellyfish."

Galna stepped up and rubbed his arm. "And I've told him I'll hunt him down if he tries to keep me out of this."

Marina smiled at the gesture. "Some of grandfather's theories were more than a bit harebrained, but your science looks solid. Just the three of us know about this right now. Your secret is safe." She trailed her hands along the glass as she circled the tank. "So, how do you handle the jellyfish?"

Galna and Check talked her through the experiment as they carried it out, while Marina corrected them according to the new calculations she'd made. At the end, a clear, syrupy fluid filled the beaker.

"Now I pour it in the mold, hold it under a UV light to harden, and voila." Several minutes later, Check held up the thick, transparent rod. "It's high-tensile. Stronger than graphene, if my calculations are correct-"

"And mine, which definitely were," inserted Marina.

"Yes, thanks to you, oh-so humble super-genius," Check teased.

Marina flipped her brown hair over her shoulder. "Hey, when you've got it, you've got it."

Check turned the rod over in his hands. "If this has worked, we'll be able to make any shape necessary. It won't break. Won't rust. Even bolts." He winked at Marina.

Galna stepped up and took it from him. Since the glass ceiling was dark with night, she held it near a glowing root. The rod lit up internally as if shining with a prism from within. "Look at that! Just imagine what it'll look like in sunlight. Besides making stronger buildings, the aesthetic applications will revolutionize architecture."

For several long moments they stood captivated.

Galna twisted open a clamp on the end of a workbench and secured the rod in place. "Let's do a field test."

Check tossed them protective goggles, then picked up a hammer. "Here goes."

He swung. A loud sproing sounded through the room and Check dropped the tool with a cry of pain. "Crap! The reverberations are wicked!"

They all examined the rod. Not a mark.

With a barely contained smile, Galna warned, "Let's not get excited. It was just a hammer. We need to do proper tensile tests."

Marina's phone chimed. She read the screen and said, "They found a replacement for Denit." She met Check and Galna's carefully blank faces, then slid the phone back into her pocket. "There's no way I'm leaving. This could clear out the jellyfish blooms and help revive the oceans. That's way more important than earning a few credits. Do we need to sneak into the Academy to use their Tensile Strength Machine?"

Check whipped a dust sheet off a machine in the corner. "We're covered."

When Marina gaped, it was Galna's turn to shrug and look sheepish. "I've been doing a lot of overtime too."

They clamped the rod in place and began applying pressure. The only sounds were the groans of the machine as it strained against the rod trying to bend it and the gentle glug of the jellyfish tank.

"The machine is at it's max. Not even a bend," Galna whispered.

The quiet shock of having achieved success filled the room.

Marina jumped and shouted. "It worked!"

"It worked!" Check chanted with her and grabbed Galna. She squealed happily as he swung her around in circles across the room, finally setting her on her feet and planting a kiss on her lips.

As they parted, she whispered, "This is the start of something big."

Keeping an arm around Galna, Check turned to Marina. "We need to go to the Academy."

Marina waved away the suggestion. "They'll find out soon enough. Forgive my hubris, but I have a different plan. I know a fisherman who can get us a boatload of jellyfish and an architect and engineer team crazy enough to build something just to see if it works."

She flashed a quick smile at Check and Galna's looks of amazement. "Contacts are the real currency of my little gambling queendom."