He’d been sampling for something in the ice, or the seawater beneath. From the numbers in the lab book, it looked as though red meant positive and green meant negative. Transferred to the map, that meant that the substance appeared in the water either at Echo Bay or at the Helbreen, flowed along the coast, then vanished.

It might have been flowing in from the glacier’s run-off. But all the circles on the Helbreen were green. Could it be something the oil company was emitting from Echo Bay?

I studied the dates next to the circles. He’d started last October near Zodiac, taking samples along the shore and out in the fjord. All green. November, December, January: he hadn’t gone far, but he’d stuck at it, picking up a couple of samples every week. What drove him? He didn’t have to be here. Why suffer months of darkness and freezing temperatures when he could have been at home in Cambridge sipping port in the SCR? Tracing my finger over the samples, I could almost feel his frustration as January slipped into February and everything stayed green. The samples became less frequent.

Then, in the middle of March, he suddenly turned up in Echo Bay. Nine samples that week alone, all ringed bright red. Nothing the next week; then the samples started marching north along the coast until they reached the tip of the island, where they went green again.

Whatever was in the water, he’d tracked it from Echo Bay to the Helbreen. Overshot, then circled back the next week to take a dozen more samples at the mouth of the glacier. All red. The week after, he carried on up the Helbreen, almost to its head on the big ice dome. Green again. The week before I arrived, said the dates. The week before he died.

‘And what did he find in the water?’ I asked the map.

My head was hurting. I went to the medical room and took two of Kennedy’s paracetamol. Then I stared at the map some more. Inevitably, I found myself focusing on Echo Bay.

The notebook didn’t give any clues to what Hagger had found in the water. The ubiquitous X, but he never named it. After my chat with Fridge, methane was an obvious candidate. But I’d read all the way through the lab book: apart from Echo Bay, he’d never tested any of the other samples for methane. And if that was it, he’d have labelled it for what it was.

I had the samples; I could always test them myself. But there are a million ways to test a water sample. Spectral analysis, gas chromatography, chemical analysis, DNA tests … You have to have some idea what you’re looking for. Otherwise, it’s needle-and-haystack territory.

But I did have one idea. Hagger found some bug in the water munching on DAR-X’s pipes, Fridge had said. And bugs aren’t that hard to find. Not if you have an electron microscope sitting on the bench.

I took some water from the Echo Bay sample and strained it through a polycarbonate filter, then stained the residue with fluorescamine dye. The fact that Hagger had all the equipment to hand gave me confidence. Then I popped the sample under the microscope.

A mass of blurry chaos appeared when I put my eye to the microscope, like snow on a television set. I turned the knob and it came into focus. That hardly changed the picture. That single drop was full of life: scores, if not hundreds of tiny organisms, twitching and swarming. Even under magnification, they didn’t look much clearer than grains of rice.

Back home, I could have extracted DNA to find out what they were. Here, I didn’t have that option. From the notebook, it looked as though Hagger had — he must have sent it back to the UK — but the tests hadn’t been conclusive. In his notes, he referred to the organisms as Gelidibacter incognita.

A quick lit search confirmed that Gelidibacter is a genus of bacteria that grows in ice and cold water; the incognita, I presumed, was for this unknown species. Why Hagger should have been so excited about it, I can’t guess. Even if it’s never been described before, it’s not exactly a new flavour of Coke he discovered. Dip a bucket in your local pond and you’ll probably find an uncategorised bacterium if you look hard enough.

I spent a couple of hours working with the microscope, checking each sample. Simple, repetitive work: exactly what I’d come here to escape from. Back home, I’d be checking the clock, looking forward to getting out to collect Luke from school. Now, I was happy to lose myself in it. It distracted me from the thought that someone might want to kill me.

At the end of it, I had some pretty conclusive results. The twelve samples from Echo Bay all contained the bugs. None of the others did, not even the ones from the Helbreensfjord. Whatever red meant, it wasn’t that.

That’s the bit I hate about science. You have a lovely hypothesis, so self-evident you know it must be true. And then it isn’t.

I filled in Quam’s form for the network account. There was a long section on how to choose a secure password: between nine and fourteen characters, containing two numbers and a capital letter (but no punctuation); not a recognisable word, certainly not a significant date. An acronym for a memorable sentence, suitably jazzed up with said aforementioned capitals and numbers, would be advisable. Writing that must have warmed his bureaucratic heart. Complete with the absurdity that after you’d ticked all those boxes, plus the one that said you would never divulge the password to anyone or write it down anywhere under any circumstances, you wrote it down on a piece of paper and gave it to Quam.

He wasn’t in his office, so I left it on his desk. Folded three times, with CONFIDENTIAL scrawled over it. I didn’t suppose he’d notice the irony.

It occurred to me he must know Hagger’s password, too. No point asking him: I could imagine the delight he’d take in preaching the gospel of data protection all over again. I thought about rummaging through his desk — surely he’d keep it on file. But footsteps in the hall made me think better of it.

I went to my room and lay on my bunk, more to avoid the pain in my head than because I was tired. It was hard to believe I’d slept for three days. Without Kennedy’s sedative, my mind wouldn’t shut up. Graphs and numbers floated in front of my eyes, even when I closed them. All scientists have a stubborn streak: we have to put the jigsaw together. Louise used to say that on a bad day, we’re all borderline Asperger’s.

Thinking of Louise reminded me how much I missed Luke. I went back to the radio room and tried to Skype him.

‘He’s playing with a friend,’ Lorna said.

‘Is he OK?’

‘Not really. I promised you’d buy him a mountain bike when you get back.’

She asked me how I was, about the fall and the crash, but I didn’t want to talk about it. Didn’t have anything to say. It’s hard to explain you’ve been in a plane crash that was a total non-event.

‘Don’t forget to post his letter,’ she said at the end. ‘He keeps asking about it.’

The air in the radio room was stale, and I hadn’t been outside (conscious) in three days. I dressed up in my ECW gear, zipped the letter in the inside pocket and headed for the door. On the way, I ran into Fridge. Apparently, high winds at Vitangelsk meant that Kennedy and Eastman couldn’t get back tonight.

‘Eastman said Doc got chased by a polar bear,’ Fridge told me. I laughed, then realised it was no joke.

‘I’d better take a rifle.’

I’d been desperate to leave the Platform. But as soon as I was outside, all I wanted was to scuttle back in again, like Plato’s prisoner who can’t stand the light outside of the cave. On the Platform, I could hide from the danger I felt around me. Out here, I was a butterfly on a card. Not forgetting the cold. I’d forgotten how bad it is: my eyes watered, my nose pinched tight. The pain in the back of my head spread all over.