In the sick green light, a human ear nestled on a large piece of cotton wool. Tiny hairs frosted the edge. Blood stained the cotton black.

Lizzie put her hands over her face.

I grabbed the box from Will and closed it, then put it back in the larger box, snapped the list shut, pressed Lizzie’s unresisting thumb against the screen to engage the lock and dropped it in the hollow under the stone.

“It’s not going to end, is it?” Lizzie whispered. “Either the saboteurs aren’t giving up … or it’s meant to be like this. Something has gone wrong with the game.” She looked at Will. “We’re going to die!”

Will patted Lizzie tentatively. “Ben won’t let that happen.” Then he swiftly withdrew to the other side of the gravestone.

Lizzie watched him retreat and took a deep breath. “You’re right. We’ll be fine. Thanks, Will.” As Will moved further away and started to scan the graveyard, she put her mouth close to my ear. “I’m sorry – I didn’t mean to scare him. I sometimes forget he’s younger than we are.”

“You didn’t frighten Will.” I raised my voice to speak to him. “Can you see anyone?”

He shook his head.

I frowned. “Shouldn’t someone have found us here by now?”

Will came back, pushed up my sleeve and directed the light on to the face of Grandad’s watch. “It’s 2 a.m. Everyone must be asleep.”

I pulled my arm back. “We can’t be the only ones moving at night.”

“The moon’s going down, the sun isn’t rising.” Lizzie looked up. “We could be the only ones.”

“Or maybe instead of staking out the checkpoints, they’re looking for camps,” Will said. “Fools building fires.”

I smiled then, suddenly, and said, “You’re telling me we got away with it?”

Lizzie grinned back. Then her smile died. “We’d better get to Carmen and Grady,” she said.

We kept low and, despite my throbbing head, I managed to leap soundlessly back over the wall, surprising Grady, who was still sitting with Carmen, leaning back on the stones, his eyes half-closed.

“Great guarding, Grady.” Will frowned and touched Carmen’s cheek. “She’s shivering.”

“She’s got a fever.” Grady got to his knees. “Did you find the next coordinates?”

“Yeah.” I checked Lizzie’s notebook, then held the torch over the map and my gut twisted. “It’s bad news.”

“What?” Grady scrambled to see.

“The next box is on the north-west headland.” I closed my eyes to banish the flickering aura that had settled into my vision. “There’s no cover.”

We were determined to get to the moorland below the summit point before dawn. I crunched bitter migraine-relief tablets as I marched into the darkness, grateful that my eyes weren’t fighting the sunlight.

“There has to be somewhere to hide,” Lizzie repeated. “A cave or something.”

I said nothing. I was focusing on putting one foot in front of the other. My belly was nauseatingly empty, my head pounded, my knee ached, my gum was still sore and my vision flickered – tiredness or traces of the migraine battling the tablets, I couldn’t tell any more.

When I knocked into Grady, I realized I was weaving from side to side. He pushed me away with a grunt.

“Sorry,” I mumbled.

The sky to the east was starting to lighten. The birds weren’t calling yet, but I could sense them stirring. Insects were crawling over my boots and I was beginning to see where I was stepping more clearly.

As pre-dawn started to lift the darkness, I felt increasingly exposed. I shivered, dank night air creeping under my jacket and making my skin feel cold and clammy.

Ahead of us the ground was rising more sharply. I stumbled on to the slope and walked on, exhausted.

“Keep a look out for somewhere we can hole up.” Lizzie touched my arm. “Ben? Are you listening?”

I lifted my head. “Somewhere we can hide. Yes.” I blinked at the hill in front of me.

My chin dropped again and I kept walking. The others could search. If I stopped concentrating, there was no way I’d be able to put one foot in front of the next, in front of the next, in front of the…

“Ben. Stop!” Grady this time.

I reeled to a stop and looked up. Will had Carmen in a fireman’s lift: her head bobbed on his rucksack, both arms dangled down his back.

Lizzie and Grady stood beside them. Behind them, a rockfall. Beyond that, a tree with deep, twisted roots and under the roots…

“Another cave?”

“I only found it by crawling inside the hollow under the roots,” Grady said, smug. “It’s well camouflaged.”

“And defensible.” Lizzie clutched her broken spear. “The entrance is narrow.”

I nodded. “Let’s go then.”

Lizzie guided me into the smell of tree roots, damp earth and insect husks. She switched on the torch, still covered with the T-shirt, and helped me take off my rucksack. The cave was more of a fissure; the roof made of snarled roots, the ground stone-pitted earth. In one corner, water trickled between rocks, leaving pockets of thick clay among the mud. The space was just big enough for the five of us and our gear – if we squeezed together. I sighed and Lizzie touched my forehead.

“Your face is all screwed up. You’ve got a migraine?”

“It’s better,” I lied.

“You need to sleep.”

Will dumped a feverishly protesting Carmen on to my rucksack. I helped her into a more comfortable position and she opened her eyes. “Where are we?”

“Cave,” I said. “Sort of.”

“Don’t worry,” Lizzie said, sitting beside her. “We’re not staying.”

You are,” Will said.

“What?” Lizzie looked up.

“You, Carmen and Grady are staying right here. Ben and I are going for the headland.”

I rolled my head towards him, too tired to lift it.

Will stretched out his legs beside me, winced and moved a sharp stone. “We can move faster and more quietly alone,” he explained. “But we need some sleep. It’s half three. Work out that riddle and wake us at four.”

“Riddle?” Grady asked.

“It’s a good one,” I said, fighting my drooping eyes. “What grows when it eats, but dies when it drinks?” My head pounded.

I fell asleep.

“You’ll need this.” Lizzie pressed a lighter into my hand.

I put it in my top pocket. I’d had just enough sleep so my brain had stopped feeling like it was filled with wasps and I could think again, but I was still light-headed.

Will crawled between the tree roots and I started to follow.

Lizzie caught my arm. “Don’t get hurt.”

“I’m not sure I can promise that.” I smiled weakly.

“Try,” she insisted.

We looked at one another, suddenly awkward.

“This is best, isn’t it?” she said abruptly.

“Yeah. You need to rest your ankle. Carmen needs time for her fever to break. Grady can watch Carmen and guard you while you sleep.”

“When do I sleep?” Grady cried.

“We’ll take it in turns, Grady.” Lizzie’s voice held an edge. “An hour each.”

Grady folded his arms and I turned to go.

Lizzie cleared her throat. “Come back safe, Ben and—”

“Watch Will?” I raised my eyebrows.

She snorted. “Hah, no… If you can’t get to the box without being seen, then leave it.”

“What about Carmen? What about getting to the end of the route?”

“We’ll have to think of another way to find help.”

Lizzie’s fingers hung in mid-air between us, as if she wanted to touch my face. Did she? What if I was misreading things? Especially after our last conversation.

“Ben?” Will hissed. “Come on.”

“I-I’d better go.”

“Right.”

I crawled out to meet Will.

Outside, the sky was still dark grey, but the stars were fading. It was half past four.

I hoisted my axe on to my shoulder, glad I wasn’t carrying my rucksack.

“Can you run?” he whispered.

I nodded and we started towards the headland.

We soon left the moor behind us, but were careful to keep the hill at our back.

“There’ll be other teams around,” Will huffed as he ran.

Jogging beside him, I silently agreed. Fires would be sleepy embers by now; we’d have no smoke or flame to warn us we were heading for a camp, and there could be teams already moving, trying to get to the checkpoints ahead of everyone else. Our feet crunched on pebble and gravel, unmade sand. Behind us the cliffs cut off as if sliced through.

We ran in step. Will was only a little shorter than me, and he kept his arms pumping in time with mine. His skin was blotchy with exhaustion, but he seemed as calm as ever.

In the far, far distance another island showed pinpricks of lights – streetlights or glowing windows … early rising farmers perhaps. If we set off a flare, someone might come to help. But if they did pay attention to the firework, would they reach us before the hunters did?

The headland was turning into a beach with flat rocks to the left and right. I caught my breath as I saw movement among the rocks, then realized there were seals around us, their dog-like faces curious but unafraid. I saw heads break the surface of the water. Barks warned others of our presence.

We kept going. The sky was lightening further now; pale grey, the stars washed out altogether.

“Ben, look.” Will pointed and we stopped. In front of us, picked out on the sand in larger, darker rocks, was a single word, in human-sized capitals: HELP. I had almost tripped over the tail end of the letter P.

“Someone was here before us.” Will rubbed his chin. “But they weren’t going for the checkpoint.”

“There’re people out there like us,” I gasped. “People who don’t want to play the game any more.”

“Looks like it.”

“Well, where are they?” I looked around. “They left their message and then ran away?” I shivered. “Maybe they were chased off.”

“Or maybe they realized it was pointless,” Will said.

“Pointless?” I stared at him.

“Have you seen anything fly by that wasn’t a bird?” Will pointed upwards. “I don’t think there are any flight paths over the island.”

I looked at the sad piles of stones. Will was right. Who was there to see the plea?

“They had to be desperate.”

Will shrugged.

“So how many teams are still hunting, do you think?” I kicked a stone, dislodging the top end of the P this time.

Will held up a finger. “The team that almost found us on the moor, that’s one. Reece’s team, that’s two.”

“Do you think An’s is still out there?” I looked around again, as if they would pop up from behind a rock.

“Could be – that’s three. And there was that girl we saw with the machete. That’s four. Somia’s team are probably still looking for them. She said it was a guy called Liam. I reckon that’s Liam Jones – team seven. Reece told Carmen he saw someone with a girl on a lead, didn’t he? So that team are sorted. Still in the game, but not after anyone else.”

“I still think at least one team would’ve dropped out at the second checkpoint,” I said.

“Probably.” Will nodded.

“So where does that leave us?” I bit a nail. “Four teams definitely hunting for ‘spare parts’.” I winced at my own use of the phrase. “One team looking for Somia, but who would probably take anyone they came across. One likely dropped out – they’re probably back at the jetty – and one ahead of us with a prisoner. That’s seven. So there’s just one team out here with us, looking for help. Who do you think it is?”

Will frowned. “You want me to guess a name?”

“I suppose not.” I started to walk forwards, preparing to break into a jog.

Will moved into step with me.

As we sped up, I glanced back at the word on the beach. I’d made a mess of it. Now it said HELL.

Will pressed his fist into his side as he jogged. “Lizzie still thinks there’s going to be help at the end,” he said.

“I know.” I had a stitch, too. It felt as if we were running so slowly, every step hampered by the sand. “There might be.”

Will looked at me. “Really?”

“There has to be someone at the end of this … doesn’t there?”

“Someone who intends to help us?”

“Someone from the Gold Foundation,” I panted. “They’ll deal with the saboteurs.”

Will blinked. “You don’t still think one of the other teams changed the boxes? You aren’t that naive…” He kept pushing forwards.

“Why wouldn’t they – for a million pounds?”

“It’s not that much money!” Will paused and leaned on his knees. “Not these days. You couldn’t even live off the interest.”

“Other people might not see it that way.” I stared at him. “You think the Gold Foundation brought us here to do this on purpose?”

Will nodded. “Why only raise the crossing every three days? Why not build it so it’s permanent?”

“Privacy – like they said?”

“A gate would be a lot cheaper. No, it’s to make sure we can’t leave until they’re ready to let us go. I could understand none of our phones having reception here, but Grady’s Iridium? They have to be blocking the signal somehow.”

“But … why?”

“I don’t know yet.” Will was irritated; angry that there was a puzzle he couldn’t solve. “We’ll find out at the end.”

I stared at him. “That’s why you really want to finish the course. That’s why you’re on Carmen’s side – so you can find out what’s behind this? You’re as bad as Grady. Sometimes you don’t get to know everything, Will.”

“Don’t you want to find out?”

“Not that badly.” I closed my eyes. “I just want to get us all home safe. That’s it.”

Will regarded me coldly. “You know you can’t guarantee that,” he said. “Use your brain. If the Foundation did set this course, will they want anyone going home and talking about it?”

I gasped. “What are you saying?”

Will looked at his pick. “I think someone got us to the island and set this course on purpose. Maybe it was the Gold Foundation, maybe it was some fake—”

“Now you really do sound like Grady.”

“I don’t know what their reasons are, but I do know that when we find whoever is behind this, they aren’t just going to help us. But they might be willing to cut a deal.”

“We agree to say nothing about the game and they get us home?”

“Something like that.” Will’s eyes glittered.

“Then hiding won’t help.” I sagged.

“If I didn’t want anyone leaving the island to tell tales, I’d be hunting down all the groups before they leave. I’m not sure the jetty is going to be safe. I wouldn’t want to be in the team waiting it out there.”

I groaned and turned to start running again, but Will wasn’t moving.

“This isn’t all your responsibility, Ben,” he said eventually.

“I do know that.” I met his cool gaze.

“You don’t, Saint Ben. Not really.”

“I’m oldest. I brought you here.” I clenched my fists.

“Lizzie brought us,” Will said. “Blame her.”

“I-I can’t.”

Will nodded. “Mother made you like this. She trained you – like a dog.”

I stiffened.

“She made sure you’d look out for me,” Will continued. “Especially after Dad left. But now you feel like you’re answerable for everything.”

“I’m not some animal,” I cried.

“I know about Cardiff,” he sneered. “Mother told me you didn’t get in, but it wasn’t hard to find your offer letter.”

I hesitated as my rage burned away. “In the recycling,” I said.

He nodded. “I didn’t ask for that.”

“Yeah, well, Mum didn’t give me much choice.”

“You can’t be my shadow for ever.” He looked out to sea. “I’ll speak to her.”

“She’s right though. I should be there for you. University will be hard.”

“Harder than this?” He gestured at the beach. “I can handle it. Look at me. I. Don’t. Need. You.” The night wind shifted his hair across his face and he pushed it back impatiently. “Give up your life if you must, but I won’t feel guilty about it.” He turned his gaze back to the distance. “I just don’t know what you expect from me.”

“You’re my brother. I don’t expect—”

“Well, don’t,” Will’s voice continued, inflectionless. “Don’t expect anything from me. I don’t owe you.”

“I-I know. I never—”

“All this ‘poor Ben, he has to look after Will’ stuff has to stop.” Will’s top lip curled and he faced me again. “I don’t know about you, but I’ve had enough of it. Don’t come to Oxford. I don’t want you there. You’ll hold me back.”

Hold you back…” I echoed, but Will was already moving, striding along the shore. “You ungrateful bastard,” I called. “My whole life revolves around y—” I stopped.

There was a seed of resentment inside me. I tried not to acknowledge it, but oh yes, it was there. And it was growing. How long before I loathed him? Before I demanded the debt be repaid?

A week ago, Will wouldn’t have had a problem with me keeping an eye on things in Oxford. But now he didn’t want me there. Why not?

I thought of the way he had called me ‘Saint Ben’. Perhaps there was room for resentment on both sides.

I jogged after him and when I caught him up, we ran without speaking, our feet thudding in time.

Finally we ground to a halt. We seemed to be alone and at the very edge of the island.

“Where is it?” I turned.

Will frowned.

“We did get the right coordinates, didn’t we? Maybe we haven’t seen anyone because we’re in the wrong place!”

“We haven’t seen anyone because it’s five o’clock in the morning,” Will said mildly.

I gripped his elbow. “Will, what’s that?” I pointed out to sea where something was being moved by the waves.

“A seal?” Will said, but he lifted his binoculars.

After staring out for what felt like a long time, he passed me the glasses. I hesitated before I held them to my eyes. For a second I thought I was seeing a seal and I started to lower the lens. Then the sea exhaled and something green billowed in the waves. A camo jacket floating around a body. As the waves shifted, a pale forearm twisted up and down. I almost leaped forwards, but Will’s arm slammed into me and then I saw what he had seen. The body was face down, moving only with the sea.

“Someone tried to swim for it.” I shook as I handed him back the binoculars. “They’re … dead.”

Will nodded. “They shouldn’t have tried to swim.” He turned me to face inland. “Don’t look. Focus. We have to find the fifth checkpoint.”

I nodded and let Will redirect my attention. Where was the box?

Shells curled in among the sand, and worm casts wound around my feet. When I moved my boots, a crab burrowed quickly away. We rotated. Nothing in view.

“It could be underwater,” I said abruptly. “In a rock pool.”

Will nodded and we started to look between the rocks, in the puddled water and seaweed.

The box was at the bottom of a dark pool of about an arm’s depth. Its chain curled around it like a tentacle and jellyfish floated on either side.

“Stingers?” I asked.

“Probably.” Will used his pick to drag the box out of the water.

We looked at it.

“You reckon this’ll work then?” I asked him, suddenly nervous.

“It had better.”

Will took the clay imprint of Lizzie’s thumb out of his pocket.

“Has it dried?” I reached out for the clay. It was flaky around the edges, but had hardened. Will unwrapped the mess of melted gummy bears, which had turned into soft gelatine. Then, while I held the clay, he pressed the gummy bear ‘finger’ on to the imprint.

“Just hope it’s a lo-res scanner,” Will said, and he pressed the fake finger on to the screen.

Nothing happened.

“Try again,” I breathed.

Will rocked the ‘finger’ over the scanner; there was an eternal pause and the screen lit up.

“Yes!” I punched the air and Will turned back to the keyboard.

“Fire,” I reminded him. “What grows when it eats, but dies when it drinks?”

He typed in the answer to the riddle and the locked-room game appeared.

“I hope this is right.” I flicked on the lighter and held the flame close to the sensor. “Nothing’s happening.”

“Give it a chance to warm up.” Will blew on his own fingers.

After a few more seconds, there was a click and the box opened.

Just like last time, the riddle and coordinates were engraved on the underside of the lid.

“Where’s the pencil, I’ll—”

“Got it,” Will said.

“What?”

“It’s easy.” He tilted his head at me. “You haven’t worked it out?”

I ground my teeth. “No.”

Will sighed. “What’s the twenty-fourth letter of the alphabet?”

“X.”

“What’s X with a friend?”

“Um …”

“XX, dummy – twenty in Roman numerals.”

“And XXX is for dirty movies. OK, I get it. What about the coordinates?”

Will shook out the creased and dirty map. “There.” He pointed and I moaned with relief – the next box wasn’t too far away. Back to the others and then another half-mile further. It would be somewhere on the edge of the loch that filled the bowl between the three of the highest points on the island.

Finally, we turned our attention to the geocache box.

“It’s a lot bigger than the last one,” I whispered. Will reached out and I caught his hand. “Why open it?”

“Don’t you want to know?” Will shook free and touched the box with his fingertip, almost reverently.

“Not really.” But I didn’t move. My eyes caught Will’s. “What would happen if…”

“If what?”

“If we just threw this box away,” I said. “The teams behind us wouldn’t know what to put in the cache. They wouldn’t have a reason to keep hunting.”

Will froze, his eyes flickering as he processed the idea.

I grabbed the box from him, stood and pulled my arm back to throw.