It wasn’t just because the Jellyfish might attack other boats, or otherwise massacre humanity – though I do feel like both of those were probably good reasons. I think it’s more because it was there. Does that make sense? I don’t know if it does. But I think we knew we needed to kill it because of what it was, and because of what it had done, and because of what it might do . . . and because of those dark shapes, the ones which would suddenly appear, and then slowly disappear into the jelly beneath our feet. None of us said that though. None of us talked about the why at all. We didn’t need to.

I just knew then, and I still know now, that if we’d left it, if we’d left it there on the sea and we’d gone inland to the safety of the castle, then we sort of wouldn’t have left it; and not just because I’d always have been thinking about it creeping slowly up that river, oozing and squeezing between its banks. I don’t think the castle would have felt safe at all. I think the hard ground would always have felt wobbly, and those secure walls would always have felt see-through, like they might move and absorb us at any time. And I think we’d also have brought those dark shapes with us. I think they’d always have been there, beneath our feet – not quite visible, but also impossible not to see. We didn’t talk about it, so I don’t know if that’s exactly what the others felt. But I think it might have been.

‘Is it . . .’ said Kate, ‘does it have to be a choice between us and the Jellyfish? Is there no way we could try and live with it?’

The Jellyfish lifted one of its tentacles high out of the water, almost as though it had heard her. The ripple of white waves when it smashed back to the surface again looked peaceful from up here, rings of foam drifting out from its body in perfect concentric circles. But it reminded me of the power, of the force of the creature. Of its dominance.

‘Only if we’re OK about always feeling under threat,’ I said. ‘And I’m not. I want to feel safe in our world.