‘I took the blame myself. To protect Louise, of course, and Luke: rationally, I knew her career prospects were better than mine. But also to impress her. I knew, deep down, our marriage was pretty far gone, but I thought the grand gesture might win her back. And I hoped it would buy me some slack with Pharaoh. Louise was always his golden girl. It had to count for something.’

Without looking, I could tell Greta was rolling her eyes at me.

‘You’re right. Louise and Richie had already started their affair: I still don’t know how they found the time. His marriage was breaking up. As soon as the scandal had died down, and his divorce came through, she told me she was leaving.’

All my memories of that time are darkness: winter afternoons, and endless nights of fights that only ended when Luke woke up in tears and I had to go to settle him. I felt as though my whole life had been fed into a shredder; I didn’t know if I could go on. A cold winter, but it never snowed.

‘I got custody — Louise didn’t contest it — and eventually finished my PhD at the Open University. I tried for a few postdoc jobs, but nobody wanted to hear from me. I ended up as an overqualified lab technician, wondering where my career had gone and doing the best I could by Luke. Just another single parent trying to squeeze through life.’

‘And she died in a plane crash,’ Greta remembered.

‘A few years ago. Pharaoh was a keen pilot. They were working in Alaska, Pharaoh had been given big money, ten million dollars from the National Institutes of Health, to set up a lab there. One day, he and Louise took off for a sightseeing trip in the Brooks Range and never came back. Some people suggested suicide — there was talk the money had gone missing and the NIH were asking questions — but I didn’t buy that. No one loved life more than Richie Pharaoh.’

‘Must have been tough,’ said Greta.

‘To be honest, it was more like finding out some distant cousin had died. Sad, but not traumatic. I hadn’t seen her in years, by then. Nor had Luke. I didn’t think much about her, or Richie Pharaoh. Until Martin emailed me.’

That wasn’t true. It never went away. I couldn’t look at Luke without seeing Louise in him. Every day at work, watching the DNA unspool on our machines — the code of life — I’d think about how my life might have been different.

But I’d already told Greta more than I ever had anyone else. There are parts of that even my sister doesn’t know.

‘It probably sounds pathetic.’

Greta shrugged. ‘Sometimes life is shitty.’

I couldn’t argue with that.

Nothing had changed on the Helbreen. I got out of the cab, wincing as the cold hit my stiff joints.

‘The crevasse was a dead end.’ Unfortunate phrasing. ‘He never went down there until he was pushed in.’

It wasn’t hard to find the moulin. Since I’d been there, someone — maybe Annabel — had roped it off, to stop anyone else falling in. I removed the barrier, while Greta fastened our climbing lines to the Sno-Cat. There seemed to be an awful lot of rope.

‘How far down are we going?’

‘Maybe twenty metres. Maybe one hundred.’

She handed me a helmet.

‘I wish I’d had this last time,’ I said, though I wasn’t really in the mood for joking. Revisiting the past had unsettled me, like when you wake from a dream just as it’s reaching its climax. Even though you’re awake, it won’t let go of you.

I clipped into the harness and walked carefully to the edge of the hole. Whatever damage they’d done pulling me out, the wind and the snow had smoothed it over so cleanly only a tiny opening remained.

‘I go first.’ Greta kicked away loose snow to widen the hole, then pirouetted around and walked backwards into it.

I flicked on my head torch and followed.

Forty-seven

You expect ice to be clammy when you touch it. Your body heat goes to work and the surface gets slick. But not in the glacier. As I lowered myself in, bracing myself against the sides of the chute, the ice remained dry as dust. Against the vast cold of a glacier, a human body doesn’t count for much.

The hole dropped a couple of metres, then angled away down a gentle slope. I crawled down after Greta, careful not to tangle myself on the rope. The tunnel was almost a perfect cylinder, as if it had been bored out by machine. Under my hands, the milky white walls swirled like marble.

The slope got steeper. Rather than waste energy, I sat down on my bottom and let myself slide, like being in a water pipe.

‘Stop!’ said Greta. The desperate voice you use to a child who’s about to run into the street. I grabbed my rope and just stopped myself bumping into her.

She leaned to one side so I could see over her shoulder. My torch beam shone into almost perfect darkness, dropping away far beyond where the light could reach.

‘Lucky you stopped where you did.’

I twisted my head to see more. Something flashed: a blade of light cutting the darkness in two. I brought the light back on to it and saw an icicle. Not the kind you get dripping from your gutters during a cold snap; this was taller than me and probably as broad at the top. At the bottom, it was as sharp as a needle. And we were going to be descending right under it.

‘Is that stable?’

Without answering, Greta went over the edge. Gripped the ledge, then became a glow of light slowly dimming. I didn’t look down.

I don’t know how long I waited there, eye to eye with the icicle. Whenever I moved my head, even a twitch, the light twisted so that the icicle seemed to wobble. Then I felt a tug on the rope. With a deep breath, I slipped over the edge. It wasn’t so bad, actually. The hole was narrow enough I could keep one hand on the descender, paying myself out, and the other steadying myself on the wall. I was terrified of knocking that icicle.

And suddenly I was hanging in air. Instinctively, I flung out my arms, flapping and waving, but didn’t touch a thing. With no hands on the rope, I fell backwards, was weightless for a moment, then jerked on the harness and see-sawed back up.

The rope swung and snagged. I heard an enormous crack above me. Whatever was holding the rope suddenly let go; I jerked down another metre, but something was falling faster. I actually felt the frigid air on my cheek as the icicle passed inches from my face.

‘Look out!’

It shattered on the floor, while I hung in space, splayed out flat like a dead man in a swimming pool. Like Hagger at the bottom of the crevasse.

‘Are you OK?’ I called.

The wait almost killed me. Then Greta’s voice came up from the depths.

‘Alive.’

I kicked my legs and strained forward until I got hold of the rope. I almost tore my stomach muscles, and I was sweating like mad. As soon as my hands had stopped trembling, I found the figure-eight descender and started paying out the line again. It was a long time before my feet touched the ground. When I did, I could hardly stand up.

Greta turned on her torch — she’d been saving the battery — and emerged from the darkness. There was blood on her cheek, and water, where an icicle fragment must have hit her.

‘I’m sorry,’ I mumbled. An apology’s rarely felt so inadequate. Greta’s face made sure I knew it.

I shone my light around. We were at the bottom of a huge shaft, as high as a cathedral, which tapered at the top like a wine bottle. I couldn’t see any way out, except a low crack just above the floor. Not even a tunnel, just a fissure in the ice.

‘There’s no way we can get through there.’

She pointed to scratches on the ice. ‘Martin did.’

We took off our ropes and harnesses. I felt that odd feeling of weightlessness you get driving without a seat belt, but there was no other option. We only had a few metres of rope left.