As he pulled out his arm, he felt something hard on the inside of the coat. A notebook bulging out of the inside pocket. Two notebooks, in fact, a green one and a brown one, and an envelope sandwiched between them that dropped on to the tent floor when he pulled them out. Still sealed, addressed in the loopy writing kids use when they’re trying hard.

He ducked out of the tent and showed it to Santiago. ‘You believe this?’

Santiago read the address. ‘Is that what this is about? Santa Claus?’

Franklin ripped a hole in the envelope, then paused, embarrassed. Santiago smirked at him.

‘Worried the real Santa’s gonna know you did a bad thing?’

Franklin slit it open with his finger and unfolded the letter inside. He read it quickly.

‘Kid wants an Xbox game and a new bike. Must be British — he says “thank you” at the end.’

‘Show it to Eastman?’ Santiago suggested. ‘Could be a Russian code.’

‘You’re a cynical bastard, Ops. No presents for you.’

‘So my mom always told me.’

Putting the letter aside, Franklin gave Santiago the green notebook and took the brown one for himself. They flicked through.

‘Get anything, Ops?’

‘If I remember the eighth grade right, sir, I’d say this looks like science. Maybe we can have the geeks check that out.’ Santiago looked at his captain. ‘You OK, boss?’

Franklin was staring at the brown notebook as if he’d been hit with a two-by-four.

‘A ham sandwich,’ he murmured to himself.

‘Come again, sir?’

He pulled his hood back, as if he needed more space around him. ‘This one’s some kind of journal.’

Phrases swam off the page.

‘Did he write his name and phone number in the front?’

Franklin went back to the very beginning and read the first line.

It’s not often you wake up to find you’ve been unconscious for two days. And survived a plane crash. And that someone wants to kill you.

I lay on the bed, staring at the grey ceiling, as pieces of memory fell into place. Each one was a minor revelation. I had no framework, no preconceptions at all. Just curiosity, like a tourist flipping through the guidebook of an unfamiliar city.

Heathrow Airport.

Zodiac Station.

Martin Hagger.

A crevasse.

The last piece I remembered was myself. Like looking up from the guidebook and finding the city all around you: suddenly, abstract facts meant something. I shuddered; I think I must have cried out loud in terror. It’s a frightening thing, remembering who you are.

I touched my neck and felt hair, stubble grown just long enough to lose its abrasive edge. I touched my head and felt a bandage.

I heard a door click open, and twisted my head round to see. Which was a mistake: someone had left a red-hot coal in my skull that rocked around when I moved.

Through the tears, I saw a man walk in, wearing a grey polo neck and corduroy trousers.

Dr Kennedy, my mental guidebook informed me.

‘How are we this morning?’ He certainly talked like a doctor.

‘Where am I?’

‘Wednesday morning. And still at Zodiac.’

Zodiac. Lying on the ground, ice crystals cold against the back of my neck. Awash with pain. A figure standing over me. A rock raised to strike.

I rubbed the back of my head. Gingerly. ‘I don’t know …’

‘Some short-term memory loss is quite normal,’ he said. As if that was reassuring. ‘It’ll come back in time.’

Another piece of the jigsaw dropped into place — and another surge of panic. How could I have forgotten—

‘I need to talk to Luke.’ I struggled up, fighting the pain in my head. The clock on the wall said ten past ten. ‘He’ll be at school.’

‘Greta’s spoken to him,’ Kennedy said. ‘He knows you’re OK.’

Greta. Another piece, though I couldn’t fit it into the main picture straight away. I lay back while he fiddled around putting some pills in a cup. I took them gratefully with a glass of water. I hadn’t realised how thirsty I was.

I caught him watching me. The panic tightened my chest. In that situation, you’re so vulnerable: anyone could tell you anything.

‘Do you remember the fall?’ he asked.

All my memories felt fake, like slide pictures in one of those old plastic View-Master things, clicking round as you squeeze the button. Click. Standing on the ice, reading a notebook. Click. An explosion in my skull; sinking to my knees. Click. A man standing over me, so big he blotted out the sun. Arm raised. Click. Leaning forward, face buried in his hood, watching me. A start as if he recognised me.

Click. White light.

‘I didn’t fall,’ I said. Experimentally, testing a hypothesis, but saying the words felt right. ‘Someone came at me.’

He tried to tell me there hadn’t been anyone else there except Annabel.

‘She’d gone behind the rocks.’ I need a wee. ‘Someone hit me from behind.’

‘You fell in a moulin,’ he told me. But there was a long pause before he said it. He didn’t look well. His face was grey; his hands were twitching.

‘Someone hit me,’ I repeated. Saying it again to affirm the memory. The View-Master slides had upgraded to video, strictly VHS, like the old tapes you find at the back of a cupboard. Skipping and jerking; bars of static raining down the screen.

Kennedy checked my pupils and tried to tell me it was all a dream. His face came so close, his beard rubbed my cheek as he peered into my eye. Shining the light through me, as if I was the View-Master and he could see the pictures inside. I could smell mouthwash on his breath.

‘I found a notebook,’ I remembered.

An unhappy look crossed Kennedy’s face. As if there were things he didn’t want me to remember. The panic inside me went up a notch. I wished I hadn’t swallowed those pills quite so readily.

He went over to the side and opened a cabinet. I couldn’t see him much — I didn’t want to move my head again — but I had the sense he’d deliberately turned his back on me. There seemed to be a lot of fumbling going on inside the cabinet.

I heard it snap shut. Kennedy reappeared and handed me a green notebook. The moment I touched it, I remembered a bright cave, light so blue I wanted to drink it. A backpack inside.

On the inside cover, I read a handwritten sentence, all capitalised. SOME SAY THE WORLD WILL BEGIN IN FIRE, SOME SAY IN ICE.

Robert Frost, my guidebook said. Strange, the things you remember.

I flipped through slowly. Pulling each page into focus hurt my head; trying to understand it was worse. As much as I knew anything for sure, it looked like a standard lab notebook. Lists of samples with places and dates, hand-drawn graphs and equations. And, not far in, a line that almost made me fall off the bed.

‘“Fridge wants to kill me,”’ I read aloud.

‘A figure of speech.’ Kennedy smacked his hand to his mouth and swallowed something. ‘Martin did some work for DAR-X. Fridge thought that was sleeping with the enemy. Fridge is a bit of an eco-warrior,’ he explained, in case I’d forgotten. Which I had.

‘And what’s “X”?’ I asked. I saw it on every page: Concentration of X, dispersal of X, flow of X. The punctuation — sharp exclamation points, heavy question marks — emphasised his frustration.

‘I was hoping you could tell me.’ Kennedy glanced at the clock on the wall. ‘If you’re feeling up to it, see if you can make anything of the notebook while I have a look at Trond. Good to give your brain something to work on,’ he added as he went out.