Within a minute of lying down on the bed Marcus was asleep, and dreaming. He was with Abby somewhere he didn't recognise. She was standing on a clifftop, her back to him, looking out over a green-blue sea. Her hair was loose and windswept, glinting gold in the evening sun. She kept trying to tuck it behind her ears but the wind loosened it again, lifting long tendrils into the air. She was like Medusa before her fall, before the snakes. No wonder Poseidon fell in love with her. Marcus moved to stand beside her. "Shall we go down?" She nodded and he took her arm to guide her down the steep cliff path.

They descended through a pink carpet of thrift and sea campion. Gannets and Kittiwakes circled them, cackling and cawing, warning them not to get too close to their precious chicks. The coconut smell of gorse was in the air, sweet and cloying. As they approached the ground the smell of the sea became stronger, though Marcus knew it was not the seawater they could sense. It was the seaweed drying and rotting in the sun, the algae blooming far out on the ocean's surface. It should have been horrible, but it was invigorating. Marcus took deep breaths, letting it fill his lungs.

Marcus had never been to the coast in real life. The nearest he'd got to a large body of water was the lake they'd landed beside. He'd read extensively about the Earth, though, and those years of knowledge were turning theory into reality in his dream.

When they reached the sand, they looked at each other and knew the other's intentions without speaking. They grinned manically as boots and socks were stripped off, trousers rolled up. Marcus sighed as his bare feet sank into the warm sand. The grains were soft but diamond-edged. They got between his toes and pricked his skin as he started to walk across the sand. Soon they were running and it became a race to reach the sea first. Abby was ahead of him most of the way but as they got close to the water's edge he caught up with her and pulled her arm back so he could push past her. The water was freezing which was a complete shock and he yelped as it splashed up his calves and turned the blood in his legs to ice.

Abby saw his pain and surprise and laughed. "That serves you right," she said. She stopped at the edge, letting each rise of the tide lap gently at her toes so she could get used to the temperature. Marcus wasn't having that, and he reached out and pulled her in so that she was as deep in the freezing water as he was. She cried out and laughed at the same time, batting him playfully on the arm. "You bastard!"

"It's better to jump right in, Abby. You'll soon get used to it."

"I don't think I'll ever get used to this," she replied, looking round at the miles of white sand and ocean.

Marcus was not so enamoured with the coldness of the sea after splashing in it for a few minutes. "My legs are starting to go numb. If I don't get out of this water soon I fear they might drop off."

"I think that's highly unlikely," said Abby with a smile.

They waded out of the water and sat down next to each other on the sand. The sun had changed colour to a fiery orange and was starting to set. Time slowed as they sat quietly, watching the sun drain into the sea, turning everything a blood red. Abby surprised him by putting her hand on his leg. It felt heavier than it should, a hot centre of mass concentrated on his thigh but radiating heat throughout his body. "I'm glad we're seeing this together," she said. He placed his hand on top of hers, lacing his long fingers between her delicate ones. "So am I," he replied. She bent her fingers so that they gripped his. They sat like that until long after the sun had disappeared below the horizon and the first stars were pricking the sky.

Marcus thought he had drifted into a much-needed sleep on the sand with Abby in his arms and was annoyed that someone was trying to wake him. He tried to push the hand away that was shaking him. A voice, tired but insistent was speaking in his ear. "Sir, sir! Wake up. She's back."

Marcus gradually came to, expecting to see the night sky above him and smell the fresh sea air. Instead there was grey metal and a smell that was indescribable and an assault on his senses. He gasped and the taste of death filled his mouth. Where the hell was he? He opened his eyes and a small, thin woman was looking down at him. Rose, her name is Rose, he thought, and then stark reality came back to him. David was still asleep in the crook of his arm and Marcus carefully disentangled himself from the boy and sat up. "Abby's back?"

Rose nodded as the welcome sound of Abby's voice came through the ceiling. "Are you there, Marcus?"

"Yes, yes, I'm here."

"Good." Marcus could hear the relief in her voice. "What's the best place for us to try and cut through the shaft?"

"Probably about where you are. You're at the far side of the room about half way along its length."

"Okay, then I need you to get everyone to the other side of the room. If you can get them under tables then do it. I don't know what's going to happen when we get through but it's possible we could collapse the entire ceiling. This whole station is very unstable."

"Okay, I'll do it. Give me a few minutes."

"You've got time; I'm still waiting for the rest of the team with the equipment. They should be here soon."

Marcus started moving the furniture across the room. The beds the patients were lying on weren't really beds, they were tables covered in folded blankets. He upturned the unoccupied ones and pushed them together. With the help of Sara, Rose and Karl he gently transferred the patients so that they nestled in the tray made by the underneath of the table. He spread the blankets over them and then placed other tables at right angles over the top, forming a shelter. He rationed out more of the food bars and the water, this time taking one for himself because he was starting to feel weak and his head was pounding.

When everyone was settled he climbed back on top of the table he'd left underneath where Abby and her team were lying. "We're ready down here."

"That's great," said Abby. "I need to be able to contact you as work progresses. Do you have a radio?"

"No. Sinclair had it."

Rose interrupted. "There is a radio but the battery is dead."

"Can you make it work, make a new battery?"

Marcus looked around the room. There was an electrical oven and the old freezer with the bodies in it. He could strip them for parts.

"I might be able to. I don't want to use any water though, there's not enough as it is."

"You're in a Mess hall – is there baking soda or anything like that? You could use that as a conductor."

Marcus looked at Rose. "There might be," she said. "I'll go and look." She came back a moment later with a box of baking soda and a knife and meat saw from the kitchen. "Will these be any help?"

Marcus nodded. "Yes, I think those will be a big help. Thanks, Rose." He shouted up to Abby. "I think there's a chance I can make it work."

"That's great. I'll keep the channel open. I hope to hear from you soon. I think we're ready up here. It's going to get noisy. You might want to make some earplugs for everybody."

"We'll do that."

Rose began tearing up some cloth they could put in their ears to deaden the noise. Marcus started taking the oven apart to salvage materials to make a new battery. He was glad to have something to occupy him while he waited for Abby and her team to break through.

On the other side of the shaft Abby was organising her team. She'd found the others still exploring the halls and corridors leading to Medical and Maintenance. Naiman was convinced he could find a way through to Sinclair so she'd left him to try and brought the others and most of the equipment back with her. It was cramped in the shaft so they'd decided to work in shifts. King and Park were taking the first turn. Abby sat away from the others, preparing to monitor the radio. She wanted to keep in touch with Marcus to keep his spirits up but mainly so she could monitor his health. She didn't think he'd noticed but he'd slurred a couple of his words a few minutes ago and she was concerned for everyone down in the Mess hall. The smell coming through the shaft was ghastly and she could only imagine what it must be like in the room. It was slowly poisoning everyone in there.

She had no idea if they were going to be able to get through the thick metal of the floor. The only sharp tool they had was the pickaxe. They were going to try and introduce a weakness to the metal by repeatedly hammering it at one point. Once they'd broken through they would try to widen the hole and work the spades in to peel back the metal. The problem was most of the Ark was made from titanium, Kevlar and high grade steel. It was designed so that it couldn't be punctured by meteoroids or other space debris. King suspected that the maintenance shaft was made of a lower grade steel and aluminum and the entire operation was based on that supposition.

King looked over to her. "We're ready, Chancellor."

She nodded. "Let's do this." She watched as King raised the pickaxe as high as he could and brought it down on the floor in front of him. It barely made a scratch. He looked up at her. Abby gave a smile of encouragement. "Keep going. It's just going to take time." And a lot of effort, she thought. Time was the one thing they didn't have and energy would soon run out with the amount of effort required.

Half an hour went by and King gave the pickaxe to Park for her shift. He had managed to puncture a small hole in the metal but his torch just picked out what was one of presumably many layers beneath it. Still, the small breakthrough was encouraging. Abby had heard nothing from the radio but then in one of the pauses between pickaxe strikes she heard a crackling and Marcus's voice came through faint and full of static. She moved further away from the team so that she could hear him.

"Abby?"

"I'm here, Marcus. I can barely hear you, though."

"The battery isn't very strong."

"Well, it's better than nothing. You've done well."

He didn't answer but she could hear him breathing, loud, shallow breaths that concerned her. She kept her voice light. "How is everyone down there?"

"Not good. We've lost one, Peterken, from Tesla station originally. He was the oldest, and the weakest. He was already ill, before…" Marcus's voice trailed off.

"Marcus?"

There was silence for a few seconds and then his voice came through again. "How is it going up there?"

"It's going well," she said, trying to inject confidence into her voice. "We're making progress."

Marcus wasn't fooled. "Don't lie to me, Abby. I need to know the truth."

"We are making progress. It's going to take a while; hours, probably."

"Okay. Well, we're not going anywhere."

"That's true. Save the battery. I'll speak to you again in another half an hour." Abby clicked the radio off and looked at the tiny hole in the metal with frustration. How could they be so near and yet so far?

The next few hours followed the same pattern. Every half hour there was a shift change and Abby would talk to Marcus over the radio. The hole in the floor got gradually wider and deeper. The tunnel became hotter and more airless. Everyone was exhausted, dripping with sweat and tempers were becoming frayed amongst the team with arguments about technique and how many layers of metal were left. Abby had taken a turn with the pickaxe and it had nearly destroyed her. The restricted space meant she couldn't get a full swing and let gravity help power her arms. Instead she had to use all the strength she could muster to hammer down on the metal. It was the most physical work she'd ever done in her life.

Back in her relatively quieter section of the shaft Abby switched the radio on again and called for Marcus. It was taking him longer to answer every time. He was sleeping in between conversations and although no one else had died he'd told her that four of the patients had slipped into comas and no one else had much energy left. She had decided to try and keep him talking to keep him awake and alert as long as she could.

His voice crackled over the radio, heavy with sleep. "Hey."

"Hey. How is everyone?"

"Same."

"Have you eaten anything?"

"No."

"Then do it now. You need to keep your strength up." She could hear the rustle of paper as he tore open a nutritional bar.

"There's not much left," he said.

"No. It won't be long now. Drink a little."

"He worked with my father, you know."

This comment came out of left field. Abby didn't know what he was talking about. "Who did?"

"Peterken, who died."

"Oh, right. Yes, you said he was from Tesla station. That must have been a long time ago."

"I thought I recognised him, and then I remembered. He came to our quarters sometimes. He was younger. My age."

"Not that young, then," The radio fell silent. Abby didn't think it was her poor joke; he had probably nodded off again. "Marcus?"

A few more beats of silence that sent fear running through her veins and then "Hmmm?"

"What do you remember about him, your father?"

"Strong. Tall. Tough."

"Like you."

He gave a small laugh. "Hmm. Not back then."

"No, you were a scrawny kid."

Another laugh. "Yes. I wanted to be like him, especially after he died."

"That was a tough time. I remember." Abby remembered it well. The Guard marching in to the Mess Hall while they were all having dinner, taking him away in handcuffs. Young Marcus sitting in silent shock, Vera screaming. He was never seen again. Justice on the Ark was swift, always had been; except it wasn't justice, because he was innocent. By the time everyone realised that it was too late. There was a question Abby had always wanted to ask Marcus but never dared, about why he had been such a vehement supporter of the powers that be after what happened. The subject of his father had always been a closed book. She thought about asking it now, as he seemed to be opening up, but it didn't feel right, like she was exploiting his condition. She tried to lead him gently to the subject in the hope he would answer it without her asking. "He never got a pardon from the Chancellor, after they found out the truth."

"No. What would be the point? Too late by then."

"The point being that it was a miscarriage of justice. They got the wrong man. He didn't deserve to die."

"He did under the rules of the Ark at the time. They thought they had their man. They did the right thing by the law."

"Do you really believe that?" There it was, the question, sort of. Her pulse quickened.

"It was what he believed. The law is the law; the future of the Ark depended on it. That's what he taught me. You can't change the laws just because it becomes personal, Abby, or it's someone you care about. He wouldn't have wanted that."

No one knew that better than Abby. She'd watched as her own husband was floated for a crime he never really got around to committing. She'd been in the airlock herself as Marcus tried to send her into oblivion with a nod. There was little room for sentiment on the Ark, but that's where they went wrong, she believed. They were too strict, too rigid, and it didn't stop people when they were desperate. Nothing ever would.

She persisted with her original question. She needed to know his answer. He'd changed, since the Ark, but maybe not as much as she'd thought. "Is that what YOU believe, even now?"

There was a long pause while he thought about his answer. "I think perhaps there are more shades of grey than I realised."

"Maybe even a little colour?"

He sighed deeply. "You're the colour," he said quietly.

Abby was flustered. "What do you mean?"

He didn't answer directly. "My father… I never wanted to get close to people after. Hurts." He yawned. "Tired."

"Try to stay awake, Marcus. Do you still feel that way?"

Another long silence, then: "Not s'much."

"What made you change your mind?"

This time the silence didn't end. "Marcus!", "Marcus!" There was no response. Tears fell and she let them. She was exhausted and her mind couldn't help whirring through all the terrible outcomes oxygen deprivation and pulmonary toxicity could bring – organ failure, sight loss, brain damage, death. If he'd slipped into a coma then with the limited equipment and supplies she had there was little chance of getting him back.

She scrambled to her knees and crawled as fast as she could over to King. "We have to get through NOW! We can't wait. Please hurry."

"We think we're nearly there but then we have to make the hole big enough to get through."

"How long is it going to take?"

"It's impossible to say. At least another hour."

"We don't have another hour, King. They're dying down there."

"I know, Chancellor, but we're doing the best we can. Everyone's wiped-out."

"Try harder!" Abby spat the words out. It was mean, she knew, because they were trying but it wasn't good enough. She wanted to rip through the metal with her bare hands.

She watched helplessly as the team continued to work. After fifteen minutes the hole was big enough to see through. King shone his torch through the gap.

"What can you see?"

"Just the floor. The hole isn't big enough to see too far into the room."

"Abby took the torch from him. "Let me see."

"Be careful, Chancellor, the metal is jagged. It's not safe."

She lay down and tried to peer through the hole. No matter what angle she shone the torch at King was right, she could only see a small radius beneath. She shouted Marcus's name over and over but there was no response.

King took the torch back from her and gave her what he must have thought was a comforting smile. "It will go quicker now, believe me. We'll soon be through."

The next hour was torturous. She was so on edge she couldn't sit still. Her feet were tapping a crazy rhythm on the floor, her hands were fidgeting with her hair, cleaning dirt out of her nails, picking flecks of muck off her clothes. Anything to keep her mind occupied. And still she watched as the hole grew bigger and King started to flatten the edges to make it as smooth as he could.

Finally, he looked across to her. "It's ready."

Abby flew across to the hole and looked down. Marcus had left the table beneath and before anyone could stop her she dropped down into the dark of the Mess Hall and landed with a painful bump on the hard surface. "My bag," she shouted back, and King dropped her medical kit down after her. She shone her torch around the room and the beam picked out the huddle of people at the far end of the room, sheltered underneath a haphazard arrangement of tables. The smell was overwhelming and made her gag. She couldn't see Marcus at first. He wasn't under the tables with the others. She found him lying a short distance from the rest, curled into a foetal position with the radio still clasped in his hand. She shook his arm and whispered in his ear. "Marcus. Wake up." There was no response. She leaned in and took hold of his wrist. She struggled to find his pulse but after a couple of seconds she could feel a faint breath on her cheek. He was still alive, but non-responsive. There were thuds behind her as the rest of the team jumped down and ran over to help the other patients.

She brushed damp curls of his hair away from his forehead and rested the back of her hand on his brow. He was hot but she didn't think it was from fever. It was stifling in the room and he was overheated. She gave him a shot of atropine to counter the effects of the toxic air and increase his heart rate. She got some water from her pack and wet his dry lips with it. "Come on, Marcus. Wake up, you can do this."

She kept shaking him gently until he started to stir. He slowly opened his eyes and looked at her, his brow knitted in confusion. "Abby?" He tried to sit up but didn't have the energy so she sat down beside him and pulled him towards her so that his head rested on her chest.

"I'm here," she said. "Have some water, it's the best thing." She held the water bottle to his lips and he took a drink.

"You made it through." He sounded amazed and Abby was as well now that she had time to think about it. Finally after days of searching she had found him, and it felt good having him in her arms. She squeezed him a little tighter before letting him go. "I have to go and check on the others. Keep sipping the water and eat these. You need to get some strength quickly for the journey out of here." She gave him nutritional bars and packs of seeds and reluctantly left to examine the other patients.

She found two more bodies, a man and a woman. She got Park to move them and the elderly man she presumed was Peterken to the back of the room. Two other men were in comas and unresponsive. She thought it unlikely they would survive the journey back to Arkadia but she had to try. King was examining a young boy of about ten who was slowly coming round. She went over to him.

"Hi. My name's Abby. What's yours?"

"I'm David."

"Hi David." Abby examined his heart rate and his pupils. He seemed to have survived better than any of the adults. Kids always amazed her with their resilience. "How are you feeling?"

"I have a headache."

"That's to be expected. Take these tablets with some water. They'll make you feel better. It's a bit smelly and horrible in here, isn't it?"

David nodded, swallowing the pills. "Where's Mr Kane? Can I see him?"

"I'll take you to him, but he's not feeling well, so be gentle okay."

David took her hand. "I'll look after him."

Abby smiled as she led David to Marcus who was sitting up on his makeshift bed, looking more awake. "Someone to see you."

David flung himself on Marcus and she saw him wince in pain although he didn't say anything. Abby didn't know why she was so astonished to see him hug the boy so tightly but she was. Marcus wasn't usually one for hugs and affection. They had bonded through their shared experience she supposed. She watched the scene for a moment, a knot of something indescribable tightening in her chest. Then she thought of his look of pain. "Your leg! Let me examine it."

Marcus shook his head. "It's fine, Abby, honestly. There's no need just now. Later, when we're back at camp."

"If you're sure."

He nodded. "I am."

Abby gave everyone chance to take on food and water and get some strength back but she didn't want to linger too long as the room was becoming unbearable. They packed up their equipment and got ready to leave. They had to tie the two comatose patients to rope and haul them up through the hole in the ceiling as the stretchers were too wide to fit through. Once they'd done that and got them settled on the stretchers they began the short journey back to the control room.

When she dropped down from the maintenance shaft Abby was thrilled to see Naiman waiting for her with Sinclair in tow. He didn't look as bad as she'd thought he would. Naiman had given him food and water and painkillers to reduce a fever he was running. Abby gave him a shot of antibiotic to be on the safe side.

Marcus limped over to his old friend and they patted each other on the back. "I thought I'd never see you again."

Sinclair smiled. "You can't get rid of me that easily. I thought you were dead."

Marcus shook his head. "Living to fight another day."

"Let's hope the journey back is easier than the one here," said Sinclair.

"It couldn't be any worse, surely."

Abby interrupted. "Shush, you two. Don't you dare tempt fate."

It only took them half an hour to crawl back through the maintenance shaft to the outside now that the way was clear. Jackson was waiting with Stevens and he ran up to Abby as soon as she got out into the open, giving her a tight one-armed hug. "I'm so glad you're all okay. It's been torture waiting for you."

"We're fine, but we need to get back to the rovers and to Arkadia as quickly as we can. No one's completely out of the woods yet."

She took up the rear of the convoy, laden down with two medical cases, a pack on her front and one on her back. Marcus hung back to wait for her. "Let me take some of those."

"I'm fine. You need to conserve your strength, and protect your leg."

"Abby." He gave her that lop-sided smirk that meant 'don't be silly'. It used to infuriate her because it was so smug and pedantic. Now it made her smile. "I can manage a backpack at least. Let me help you."

She gave in and passed one over to him. He settled it on his shoulders, thumbs tucked under the straps, and they set off back up the path towards the waiting vehicles. Neither of them looked back. They never wanted to see Arrow station again.