I was attempting a better look at the legs when the animal raised its stump of a tail. Two neat rows of holes opened up along its sides, and from these a bone-chilling sound rang out. I am sure to its own ears – or whatever sound receptors it had – the sound was as normal as anything. To me, it was somewhere between squealing metal and a dying horse. I was taught to be objective, as a scientist, but I cannot help the fact that I am also an animal with instincts of my own. Everything about the sound told me to run.

The sound wasn’t meant for me. It wasn’t a threat; it was a summons. Two more not-slugs shoved their slimy mouths into view, invited by the call of the first.

My legs were still shaky from a week and a half spent in microgravity, but I ran across the corridor anyway, entering Chikondi’s cabin without a knock.

‘There’s a—’ I began, but didn’t need to explain, because Chikondi was observing a sight very much like mine on his own window. He was watching the creatures intently, taking notes on the tablet in his lap. I sat beside him on his cot, and we watched the weird little thing push itself across the thick windowpane, leaving a trail of gummy saliva in its wake. Chikondi and I watched a new species together in companionable quiet, like we’d done many times before. For a moment, I thought that everything would be okay.

The animals were not limited to our cabin windows. We could hear more of them noisily creeping across the hull, and within an hour, every window on the Merian had at least one of the creatures slinking across to shriek awful hellos. Within two hours, you could barely see the world beyond them.

We dubbed them Fortisostium horribilis in our official report, but Jack called them rats.

‘Why rats?’ I asked.

‘Because I hate rats.’ He glared at the airlock window, nearly solid grey. There was no way we could get outside with so many creatures covering the hatch, not without potentially jamming the door mechanism with their bodies and giving others opportunity to come inside. One or two, we could shoo away. This many, we’d only be asking for trouble.

‘They’re just checking us out,’ Chikondi said. ‘They’re allowed to observe us, too. We’re the ones in their home.’

But the rats didn’t care much about us at all. It’s difficult to know what their senses were, because they didn’t have obvious sight organs, but our movements inside the ship were of no concern to them. We were scenery, nothing more.

Elena frowned. ‘They could damage the hull if they keep this up.’

‘The hull’s tough,’ I said. ‘Plus, they’re not chewing it. It’s probably fine.’

She looked at me. ‘“Probably” has a lot of room for error.’

‘Ah, get out of here,’ Jack said to the rats. He’d gone into the airlock and up to the outer door. He watched the rats for a moment, annoyed at their presence. He raised a fist and pounded the door three times in quick succession. The rats were startled by him, some scattering away, others freezing in place. Jack was encouraged. ‘Yeah, go on, get out of here.’ He pounded the door again. This resulted in more scattering, but less than before. To Jack’s consternation, other rats moved in to fill the gaps, undeterred by the angry man telling them to fuck off.

‘We’ll have to wait,’ Chikondi said. He sat on the floor and began to sketch on his tablet. The activity did not animate him, as it typically did. He did his job, but it appeared more like muscle memory than true enthusiasm.

‘I’m going to go look at the storm data again,’ Elena said to me. ‘Could you check on the comms?’

‘I already did,’ I said.

‘Oh,’ she said. She thought for a moment, visibly rifling through some list in her head. ‘What about life support?’

‘I was going to do that later, but I can do it now, if you’d prefer.’

‘If you wouldn’t mind,’ she said, though she offered no explanation as to why. It shouldn’t have mattered to Elena whether my checks were done now or three hours down the road, but clearly, it was bothering her. If I could help relieve that little bit of worry, at least, then I’d easily change my schedule. One of us needed a break that day.

I left for the upper decks, leaving Chikondi drawing by rote and Jack banging on the door.

The rats did not leave at night, nor at dawn, nor the day after. The hull was blanketed with their bodies and their spit, the combination effectively blocking out the sun. We managed to steal some looks outside, if the rats shuffled in such a way that, by chance, they left a gap in a window and one of us was there to see it. The shallows were largely featureless, but there were rocks out there – craggy pillars jutting up from the seabed like stalagmites. Jack and I took to wearing binoculars around our necks in hopes of an opening, and we eventually were able to see that the rocks were likewise covered with dense coatings of rats. In basic shape, our conical spacecraft must have seemed familiar to them: a tall thing you can crawl up and cling onto.

‘Could be mating behaviour,’ Jack posited.

‘Could be,’ Chikondi said.

‘Or some other kind of seasonal thing,’ I added. ‘External thermometers say it’s chilly out there, they might do this to get out of the water.’

Chikondi watched a pair jostle each other for space, their mouths still holding firmly to the glass. ‘Or could be this is a normal day,’ he said. ‘Maybe they just do this, and we’ll never know why.’

After two more days of staring at scaly bellies, we began to debate whether we should simply take off and find a new landing site. But we’d kill the rats in lift-off, we knew, and nobody wanted to do that, despite the obvious problem they’d become. Given the numbers we were seeing outside, though, lasting damage to their population seemed unlikely.

Opera made the decision for us. The storm system that had been so safely distant made a sudden swing south, and the winds kicked up to a speed downright dangerous for launch. The shallows swelled and roiled. Rain lashed at our windows like a hail of arrows fired sideways. We could go nowhere.

The rats hung on to us, their port in the storm. They weren’t leaving, either.

When I was a child, I was afraid of the dark. I was convinced of wicked eyes watching me from the corners, shivering hands reaching up to pull me into the void below my bed. That’s just in your imagination, my mother told me. Tell your imagination to go somewhere nice instead. So when the lights went out and the door closed, and all I could hear was my own frightened breaths, I would ask myself: Where do you want to go? The answer went through phases, depending on age and fancy. Sometimes it was a treehouse in a peaceful meadow, the contents of which grew more and more elaborate with every night that I fussed with its interior. Sometimes it was a pirate ship, with me as the kick-ass captain, waving at the merfolk who led me to treasure. Sometimes I’d build from someone else’s scaffold, replaying the best bits of a story I’d read or a game I’d played, revamping the scenes I thought could be better. The question worked, is the point, and for years, that is how I fell asleep, curled up in a nest of my mind’s weavings.

I could not sleep in Opera’s shallows. If it had been the storm alone, I could’ve acclimated to that. The wind howled like an engine, but that din was constant, certain. The rats, on the other hand . . . God, the rats. I couldn’t tune them out, no matter how I tried. The human brain is conditioned to shout danger at unseen animal sounds, opening a fire hose of adrenaline so as to awaken you to whatever prehistoric unpleasantness is about to bite your toes or foul your grain stores or drag your babies off into the night. It didn’t matter that the rats were on the other side of a wall. It didn’t matter that they were only adjacent, not in my actual space. Their sounds were unpredictable, and my brain reacted accordingly. Pushing my blankets around my ears helped with the uneven percussion of their feet, but nothing would drown out their shrieks, which they would unleash every hour, or half hour, or a few minutes after the last, wrenching me out of whatever half-formed dream I’d managed to sink into and back into puffy-eyed misery.