The door swung in. I almost whimpered with relief when I saw it was Dr Kennedy, bundled up in a snowmobile suit and a loud tartan scarf.

‘I hope I didn’t scare you.’

‘Were you worried I’d screw up the measurements?’

Kennedy shut the door and tipped back his hood. ‘I wanted a word in private. About Hagger.’

‘OK.’

‘I probably shouldn’t tell you this …’ Kennedy rummaged in his suit and produced a bottle. He offered it to me. ‘Medicinal supplies.’

I took a slug and gave it back.

‘Jameson’s,’ said Kennedy. ‘Just the thing.’

‘What did you want to tell me about Martin?’

He screwed the cap back on the bottle. ‘You know he overwintered here?’

I didn’t. Overwintering was a hard assignment, a job for grad students or people who couldn’t get any other foot on the ladder. Darkness, solitude and endless instrument readings. I’d applied for it twice.

‘Why?’

‘To get some work done. There were experiments that hadn’t gone the right way, he wanted time to sort it out.’ He fiddled with the bottle. ‘He was quite down about it, poor fellow.’

‘Four months of night would do that to anyone.’

The cap came off. Kennedy offered me the bottle again. ‘Not just in the usual way. He came to see me. As a patient, I mean.’

‘He was depressed?’

‘Clinically. Mirtazapine helped, but he was very low. Of course, he’s not the first person Zodiac’s brought down. Fridge says most people have to be half mad to come here in the first place. As I say, I probably shouldn’t tell you this. Patient confidentiality. Not that that applies, any more.’

‘And you think …’ I struggled to say the word aloud. ‘Suicide?’

Kennedy nodded. ‘Sad.’

‘Did it seem especially bad these last few days?’

‘That’s a funny thing. The day before he died was the happiest I’d seen him in months. Very excited. But that might have been a sign. You know how it goes with depression, up and down. The higher you go, the further you fall.’

Automatically, he offered me the bottle again. Automatically, I took it. I could feel the whiskey softening my thinking, lowering my defences.

‘Why are you telling me this?’

‘What you said at supper, about it not being an accident. I thought you’d guessed.’

I took it he hadn’t heard Greta’s theory. I didn’t put it to him. I didn’t want to be the next one getting happy pills on his couch.

‘The point is, we don’t want it taken the wrong way. You know there’s a lot of pressure on Zodiac’s funding. Some people think the reason we were packed off to the South Polar people was so they can shut us down.’

‘Is that Quam’s agenda?’

‘No.’ Emphatic. ‘Quam’s in charge of Zodiac, he wants to see it do well. If it goes, he’ll be out of a job with the rest of us. But he’s under a lot of pressure from Norwich.’

‘What’s that got to do with Hagger?’

‘Quam’s worried there’ll be a witch hunt. It’s no secret he made mistakes. He should never have let Hagger go out on his own — especially in the condition he was in. But if they use that as an excuse to shut down Zodiac, it’s a travesty.’

He put the bottle back in his pocket. I think it was empty.

‘They’ll debrief you when you go home tomorrow. You’ll have first bite. What you say becomes the first draft of history.’

‘You want me to tell them Hagger committed suicide?’

‘It’s the truth. Almost certainly.’

He’d said what he had to say. He pulled up his hood and opened the door, then remembered something. He came back to the table.

‘Don’t forget to take the mag readings.’ He tapped a dial to the right of the main readout. ‘It’s that one you want.’

I wrote down the numbers. Wait ten minutes, do it again, Eastman had said. I waited and shivered. The glow from the whiskey had worn off; I could feel the heat escaping through my pores. I tried a few jumping jacks, but worried I’d knock the instruments off the table.

I stared at the columns of numbers in the book and wondered if anyone ever did anything with them, or if they just accumulated. Everyone took turns: you could read the rota like the strata of an ice core in the different handwriting, the initials scrawled in the margins beside the observations. As much a record of human presence as of the vagaries of the magnetosphere.

MH. Martin Hagger. He’d stood in this frigid hut just like me, swinging his arms to keep warm, watching the clock count ten slow minutes before he could go back inside. He’d probably stood in the exact same spot.

For the first time, I really felt his loss. More than carrying his body, or clearing out his lab, the simple act of occupying the same space, only time between us, brought me closer to him than I’d been in years.

Why did you fall? I asked him.

I liked Kennedy; I wanted to believe him. I didn’t like Quam, but at a stretch I’d have taken his polar-bear theory. I’m a scientist. At science school, as Greta would put it, you’re taught the simplest explanation is the best. Occam’s razor.

But you can’t change the data. Whatever pressure Hagger had been under, whatever black cloud, I didn’t think he’d roped himself up in that harness just to throw himself in. And Greta had convinced me the polar-bear theory didn’t hold up.

What happened to the notebooks?

Why did he have his gun out?

Why did he bring me here?

Questions chased around my head like snow devils blown by the wind, and in the end it all came back to the same place. In twenty-four hours I’d be in the slush and drizzle at Heathrow, and Utgard would be a bad dream. I’d tell the bureaucrats that Hagger’s suicide was an unavoidable tragedy. Perhaps Quam would write me a reference.

Ten minutes were up. I wrote down the number, noted the time and signed my initials. One more layer accumulated in this freezing room.

Outside, my eyes struggled to adjust. Hemmed in by mountains, the twilight was darker here than it had been up on the ice dome. The red eyes on the radio masts blinked their warnings. Slivers of yellow light showed behind the gaps in the blinds on the Platform. I’d read some experiments that had been done here in winter, measuring exposure to artificial light. Apparently, there wasn’t even enough to convince the body’s clock to wake up.

I hurried back towards the flag line. Then stopped. Above the drone of the generator, I’d heard the snap of the snow crust cracking underfoot.

‘Who’s there?’ I called.

No answer.

‘Dr Kennedy?’

I couldn’t tell where the sound had come from. I couldn’t see anything. In the jumble of rocks and buildings there were plenty of places to hide.

I started running, back to where I’d left the gun. I reached the flag line — but the gun wasn’t there. Had I missed it? I’d followed my footprints.

A few yards away, a figure reared up from behind a cache of oil drums. Something flew out of the gloom — I barely saw it — and hit me bang in the face. I screamed and dropped to the ground.

Wet snow trickled down my nose and on to my lips. Eastman advanced from behind the barrels, one arm cocked back holding a snowball. He grinned, and pitched it at me like a baseball. I tried to roll out of the way but it smacked me on my ear.

‘Gotcha.’

I overslept. No one came to wake me, and the light creeping round the wardrobe wasn’t enough to break into my dreams. When I did open my eyes, and found my watch, I stared at the dial almost incapable of understanding time. I’d missed breakfast. If I wasn’t quick, I’d miss the plane.

I threw my clothes into the bag. There wasn’t much to pack. I’d just about finished when there was a rap at the door.

‘Plane’s cancelled,’ said Quam. ‘Bad weather.’

I peered at the crack around the window. The sun was shining; I couldn’t hear any wind.