THE SKY WAS clear and the moonlight turned the world to a muted black-and-white photograph. It was just past midnight, the time Alice had specified, and the boys moved swiftly down the street. Their backpacks swung from side to side. They were stuffed with the items Alice had told them to bring, stolen from the camping cupboard: high-energy snacks, headlamps, a water bottle, strong walking shoes, a jacket each, a sharp knife and warm sleeping bags. Nothing stirred. No cars passed, no curtains twitched, no strangers walked their dogs.

‘Over there, that’s where she said. Come on.’ Stefan pointed across the road to a real-estate sign, bravely offering a ‘Shady Hideaway’. The sign was set against a steep bank where the hill had been cut through to make way for the road. Even by moonlight it was plain that this was not a promising place to begin a search for a tunnel. There was nothing but gorse clinging to the sheer side of crumbling rock. But a promise is a promise, and the boys crossed the road, their brisk walk turning to a run at the sound of an approaching car. They dived behind the ‘For Sale’ sign just as headlights swept around the corner, brushing the road clean of shadow. Arlo pulled his head down to his chest and held his breath, waiting until he could hear the car taking the next bend before looking up.

‘You’re late.’ Alice was curled behind a clump of long grass, her dark form folded perfectly into the dirt and rock.

Arlo gave a start. ‘You’re lucky I didn’t land on you,’ he said.

‘You’re lucky you didn’t land on me,’ she answered. ‘Did you get everything I told you to bring?’

‘We have everything,’ Stefan said. ‘But it’s like we said, we have to be back before three. So whatever it is, you’re going to have to hurry.’

‘You’ll be back in bed before three, I promise,’ Alice told them, but there was something about the way she said it, the secretly pleased voice a person uses when they’re delivering a riddle, that made Arlo think they were being tricked.

‘Where are we going?’ he asked.

‘I told you. Through a tunnel.’

‘What tunnel?’ Stefan challenged. ‘There aren’t any tunnels around here.’

Alice looked quickly up and down the street then stood up. Her eyes seemed to glow for a moment and she whispered, ‘It’s right behind you.’

That was ridiculous, of course. Both boys had walked this way a thousand times and there was definitely no tunnel through the bank. They would have seen it. Everybody would have seen it. But they both felt the oddest sensation: a warm wind at their back, followed by strange smells they couldn’t quite place, smells that couldn’t belong here.

‘It’s opened. I knew it would!’ Alice couldn’t hide her excitement. ‘Come on. Quick, before it closes up again.’

Stefan had noticed this before, the way the times you most need to ask a question are so often the times when it’s hardest to get that question out. It wasn’t just one question, he had a hundred of them. A tunnel entrance the size of a small child doesn’t just open magically in a rock face without you having questions. But Alice was pushing Arlo into the opening, and scrambling close behind him, so his questions were going to have to wait. He did however think to grab his headlamp from the side pocket of his backpack before following the soles of Alice’s worn sneakers into the darkness. He was frightened—his body prickled with anxiety—but he was excited too. It made life difficult, the way those things so often mixed together in his blood.

Up ahead Arlo put on his headlamp and the roughhewn walls of the tunnel danced beneath twin beams. The walls were cold to touch but the warm breath of strange air pulled them forward.

‘How long is the tunnel?’ Stefan asked, dropping from stoop to crawl as the walls and ceiling closed in. The ground was rough and he felt sharp stones digging into his knees. He thought of Arlo at the front, terrified of weta and spiders, doubtless pushing ahead with his eyes scrunched and his shoulders drawn tight to his neck.

‘It opens out in a moment,’ Alice said, as if this had been his question, before adding a cautious, ‘I think.’

‘You’ve been here before though, right?’ Stefan checked.

‘Yeah. Once.’

That can’t have been right. With a tunnel you either went through twice, or you were still on the other side. Stefan added this to the list of questions he needed to ask and turned his attention back to the tunnel. As far as he could see it was clean of insects, which was strange, and it was widening, just as Alice had said it would. Indeed it was now high and broad enough for Arlo to stand in the middle and turn back to his fellow adventurers. Stefan saw from the expression on his face that he was not frightened at all, but buzzing with the excitement of such a strange midnight adventure.

‘Isn’t this incredible?’ Arlo whispered, as if speaking too loudly might break the spell and return them to their uneventful beds. Then he turned to Alice, his eyes ablaze with curiosity.

‘Who made this tunnel, and why haven’t we ever seen it before? And where is it taking us?’ Arlo had a way of asking his questions in mouthfuls.

‘I don’t know who made the tunnel,’ Alice said. ‘But the reason you haven’t seen it before is that it isn’t usually here. It only appears on a full moon, and only for identical twins.’

That couldn’t possibly be true, but then again they were standing together in the middle of a tunnel that shouldn’t exist. ‘And as for where it leads to, you’ll see it for yourselves soon enough, so it hardly matters. Come on, I don’t know how long the tunnel stays open for. If you turn off your headlamps you’ll see a light ahead.’

They did as they were told and sure enough a thin slit of light shone ahead of them, exactly as it had in their dreams.

Stefan shivered. ‘What’s making that light?’ he asked.

‘Sunlight,’ Alice answered.

‘But it’s—’

‘Come on, hurry up.’

The going was easier now that they could walk upright and they moved quickly towards the light. The warm wind strengthened with every step and by the time they stopped again it was whistling all around them. There were snatches of sound too, hints of voices and movement. The light and wind both originated from the same source, a horizontal gash in the rockface, half a metre higher than their heads.

Alice pointed upwards, raising her voice above the wind. ‘That’s it. That’s the exit.’

‘How do we—?’ Arlo started, but Alice was already crouching, her hands together in a cradle ready to boost the foot of the first boy to volunteer. Arlo stepped forward.

‘On the other side you will tumble into long grass and bright daylight,’ Alice told him. ‘Stay lying down, hidden from sight. Do not move, do not make a sound. Your life depends upon it. Do you understand?’

Arlo nodded, and looked at his brother. If they were going to turn back, he was pretty sure this was the moment to do it. Neither spoke. They had made a promise.

Arlo put his foot in Alice’s hands and his hands on her shoulders and stepped up against the wall, reaching for the opening. He pulled himself forward easily. Arlo was a strong climber; they both were. The wind whistled about his ears and he turned away from the blinding light, lowering himself backwards into the grass. He lay still, barely daring to breathe, taking in the heat and smells of summer, and a medley of noises that made no sense to him.

Stefan was next. He waited on the ledge then reached down to pull Alice up. She was strong and agile too. She hauled herself up beside him and nudged him forward. ‘Go on then.’

Stefan lowered himself from the gap, settling into the grass beside his brother. Alice quickly followed. They squirmed together, heads in a circle, the boys awaiting their instructions.

‘All right,’ Alice began. ‘Whatever happens, nobody can see the two of you together. Never. That’s the first rule here.’

‘Where are we?’ Stefan asked.

‘I don’t know. But it’s…’ Alice paused, as if uncertain how to explain it. ‘Look for yourself. But be careful.’

The boys lifted their heads and knelt, parting the long grass before them and peering out onto a world that was both completely strange and yet somehow familiar. Beyond the grass was a wooden fence made of twisted manuka branches bound roughly together with thick, oily rope. Past that was a dirt track, winding its way down to the shore. A low tide had exposed wide mudflats, and beyond them, on the other side of a deep channel of water, was a hill, capped by a great structure that glowed white in the sunlight. Stefan squinted and tried to make it out. It looked like a huge tent, the sort you might see at a circus, but without any of the gaudy colours. A sailing ship moved quietly through the channel towards a broad harbour. From its rigging, men shouted instructions to one another, although they were too far off for Arlo and Stefan to make out what they were saying, or even what language they were speaking. The air was tinged with the smell of seaweed and something burning. To the south a great black pillow of smoke hung low over a long stone wall.

The sound of footsteps pulled them back from their confused fascination. A young man with baggy trousers and the kind of cap you only saw in television shows was walking down the road, kicking at stones and whistling to himself. The brothers instinctively drew back into the grass. As the boy drew nearer the twins turned to one another, to check they weren’t seeing things.

‘That’s…’ Arlo started, but he was too stunned to finish the sentence.

‘I know,’ Stefan whispered, pulling further back from the road. There was no doubt about it, the boy walking slowly past them, kicking a stone with seemingly not a care in the world, was Mike McGuiness.

‘But it can’t be,’ Arlo muttered.

‘It is,’ Stefan replied. ‘And I’ve noticed something else too. Look around you. Look at the harbour, and the shape of the hills. Look out to the island.’

Beside them Alice said nothing. What they were experiencing, she too must have been through, and now she was leaving it to settle on them in the same way. Arlo looked again at the road, the trees, the hills, the rush of water now filling the inlet and the broad, rock-strewn bay beyond, but still he didn’t understand. It was all new to him, new and strange.

‘The island,’ Stefan repeated softly. ‘Look at the island.’

Arlo looked to the west where his brother was pointing. The northern end of a low island, its top so flat it might have been sliced off by a gigantic knife, poked out from behind the headland: an island so familiar the sight of it was immediately comforting.

‘Mana Island!’

Slowly it dawned. Arlo looked about him with new eyes. It wasn’t just the island that was the same, it was everything. The hills, the inlet, the harbour, the overgrown bank. Yes, the houses were missing, and the roads, the double bridge and the train tracks. Where there should have been a radio mast there was a strange tent, but there was no denying what this place was. They were still sitting at the side of the road in the very suburb in which they lived, at the very spot where the ‘For Sale’ sign had been erected. Only the sign was no longer there, and it wasn’t the middle of the night anymore. It wasn’t any time at all.