(The values Hagger got fluctuate, but for the red samples they mostly sit in the high hundreds. In the green samples, next to nothing.)

‘If he knew the measurements, he must have known what he was measuring.’ I waved my hand around the room. ‘The thing is, I can’t work out how he did it. To test that many samples he’d have needed chemicals, titration equipment, maybe a mass spectrometer.’ Even knowing what he used would give me a clue what he was looking for. ‘There’s nothing like that here.’

After a moment, I realised Greta had gone quiet. I mean, she’s never exactly forthcoming, but this was a more deliberate silence. Provocative, almost.

‘What?’

‘I know where Martin kept his equipment.’

A shadow went through me when I saw the crucified Buzz Lightyear toy nailed over the door of the caboose they call Star Command. Luke has one just like it. But I forgot it the moment I stepped through the door.

There was a mattress on the floor, raised off the ground on a couple of pallets. Two sleeping bags zipped together on top of it. Most of the rest of the room was taken up with a table, and the three machines on it. They didn’t look much different from desktop printers, or maybe a fancy water cooler. One was a mass spectrometer. One was a thermal cycler for replicating DNA. The third was a DNA sequencer. Hagger’s usual mess filled in the gaps: test tubes, spare nozzles, used chemical hand warmers that looked like teabags, and half a dozen empty plastic bottles.

‘Why didn’t you tell me about this before?’

Greta gave me a hard look. I glanced at the mattress again, with its double sleeping bag and twin pillows. The caboose would be a cold place to sleep; you’d freeze if you tried to undress. But maybe two people could warm it up a bit. If they wanted some privacy.

That wasn’t my business. ‘Do you know what Hagger was doing here? With the instruments?’

‘We didn’t talk much about work.’

It took an effort of will not to look at the bed again.

‘That’s a DNA sequencer,’ I said, in the too loud voice of an embarrassed Englishman. ‘He must have been trying to sequence that little worm he found eating DAR-X’s pipes.’

Greta gave the sequencer a once-over, with the practical eye of a mechanic. I got the feeling she was wondering how it would come apart.

‘I thought he was a chemist.’

‘Biochemist,’ I corrected. ‘Sort of both.’ I wondered how much she knew. ‘Martin worked at the boundary of biology and chemistry. What he was interested in, what made him famous, was his work on the origins of life question.’

‘OK.’

‘Maybe you’ve heard of the idea that life evolved in the tropics, in nutrient-rich pools. You’ve heard the phrase “primordial soup”?’

If she had, she was giving nothing away.

‘Martin didn’t agree with that. He used to say that putting all the ingredients in the bowl doesn’t make a soup. Someone has to stir it. He believed that the cycles of the Arctic sea ice, freezing and melting and freezing again, year after year, were what stirred up the soup and made the ingredients mix.’

If that sounds fluent, it’s because I used to hear Hagger give the same spiel, time and again, when I was in his lab. And, almost always, get the same objection.

‘There’s no life in the Arctic.’

‘That’s not true. When the sea ice forms, the salt in the seawater gets left behind. Gradually, the water that remains gets saltier and saltier, until it’s too salty to freeze. The ice forms a crystal lattice, with tiny holes in between where the supersaturated salt water stays liquid. And each of those holes is effectively a test tube, where any DNA particles in the water can combine and replicate to their hearts’ content. When the lattice melts, the DNA’s released into the wild, until the seawater freezes again. And each time, those strands of DNA get a little longer, until eventually they cross the threshold and become life.’

‘It’s a magical time,’ said Greta.

‘The point is, Martin found proof. Here, at Zodiac. The sea-ice samples he took a couple of years ago — when he analysed them he found that stray DNA in the water was mutating and recombining at an astonishing rate. Off the scale.’

Off the scale. Like the graph Hagger had drawn of those bugs.

‘He took the samples back to Cambridge and ran some experiments. Basically, popping them in and out of the freezer a few hundred times and then seeing what was there. He’d nailed it: the longest strand of DNA ever observed naturally forming.’

I remembered reading the paper when it came out in Nature. I’d like to say I was happy for him, but that wasn’t exactly true. I’d wondered what might have been if I’d stayed with him, not switched my supervisor all those years ago. Maybe it would have been my name on that paper as first author, my lab drowning in money from all the funding bodies dying to be associated with my research. Maybe even my wife toasting me with champagne, explaining to Luke what all the fuss was about.

And maybe it would have been me lying at the bottom of that crevasse, said the bit of my brain that picks holes in everything.

The wind had risen and I’d forgotten my goggles. Walking back to the Platform from Star Command, I had to shield my face with my glove, eyes screwed almost shut against the ice that found its way inside my hood. The clouds were so low you could hardly see the far side of the fjord. I’d never imagined that perpetual daylight could get so dark. On the roof of the Platform, I could see some of the antennas bending like whips. A good day to be inside.

A folded piece of paper had landed on my desk. A mobile phone number with a +44 prefix, in handwriting so bad it could only be a doctor’s. Underneath he’d written, Burn after reading. I assumed that was a joke.

I rang the number from the radio room. After a week in the Arctic, the homely brrrr-brrrr of the phone ringing sounded like a message from Mars.

K-Mart answered with a cheerful ‘Yuh?’ that became a guarded ‘OK’ when I told him who I was. I didn’t expect any more. I’m the man who took his job.

‘Is this about the compromise agreement?’

‘Martin Hagger’s dead.’

‘Wow.’ He sounded winded. ‘That’s … I had no idea. I’ve been on holiday. I am on holiday,’ he corrected himself. ‘Wow.’

‘I’m trying to tie up a few loose ends in his work.’ Like: Why did it get him killed?

‘Right. Yeah. Of course.’

‘He died before I got here, so I didn’t get a chance to speak to him.’

‘Uh-huh.’

‘I wonder if you can tell me what exactly he expected me to do here.’

A long pause. ‘You probably know more about that than me.’

‘He didn’t tell me anything.’

‘Well he didn’t tell me, for sure. Just told me to pack my bags.’

‘Because of your tooth.’

His voice got less laid-back. ‘There was no tooth. That was a story he and Doc put together. Something to do with funding, procedure, something like that. The truth is, he wanted to get rid of me because he thought you knew more than me.’

‘I didn’t …’

‘I don’t care,’ he said, in the voice of someone who does. ‘He was the worst supervisor, just gave me donkey work. Running around the island, collecting samples. Wouldn’t even tell me about the enzyme.’

‘What enzyme?’

Ignored. ‘Look, I’m sorry he’s dead and no hard feelings and all that. But you’re the one who wanted the job. You figure it out.’

‘I didn’t want it,’ I objected. But he’d hung up.

While I was there, I logged on to the computer to Skype Luke. It took so long to connect I gave up; then, just as I stood to go, he appeared on screen. He was wearing his Spiderman costume over his school uniform, and he looked sad. It made my heart break, in a minor way. Superheroes and children shouldn’t look so unhappy.

‘The lady said your plane crashed.’

I gave one of those artificial smiles you give children, and twisted my head one way, then the other. ‘See? No damage.’