‘Do you think they went up the river too then?’ said Kate.

‘What, instead of going out to sea again?’ said Lana, her eyes wide and sarcastic.

‘It would have been weird if they hadn’t gone up it,’ said James, ignoring Lana. ‘It would have been an easy route inland for them.’

The freshwater and the seawater mingled here so you couldn’t see a division between the two. I know that’s what rivers do, and the whole point of them is that they flow down through land until they eventually get to the sea, but I didn’t like the idea of the river and the sea joining. The water was smooth and glassy, with stagnant layers of foam and rubbish bobbing gently along the edges. It looked slow-moving and peaceful, but here and there in the brown water there were whorls of fast-swirling sediment, some with leaves or twigs caught, twisting round and round on the surface. Places where the sea was pushing against the river water, trying to get inland.

I wondered how easy it would be for other things to travel up the river – things which weren’t boats. And I wondered how far up the river the saltwater went.

‘Come on,’ said James, ‘let’s walk faster.’

‘I think—’ said Kate.

‘Oh god,’ said Lana, ‘stop thinking. Please. Just shut up!’

‘All I’m saying,’ Kate was already sounding defensive, ‘is that I think we should go back for the sheep. They’re creatures too. With feelings. And I don’t like that we’ve just left them on the Jellyfish. If I’d known that, then I wouldn’t . . .’

‘Wouldn’t what?’ said Lana. ‘You’re not going to say you would have stayed on the Jellyfish with them, are you? Because I know that would be a lie.’

‘I just feel really sad,’ said Kate. ‘We didn’t even leave them any grass. And I don’t know if they eat fish.’

‘They eat seaweed,’ said James. ‘They definitely eat seaweed. I saw them.’

‘Oh. OK,’ Kate was placated slightly.

I don’t think they eat seaweed, James mouthed at me and Lana.

We’d started out in our new clothes and trainers by jogging at a distance from one another; our garden forks were in our hands, because, you know, that way if one of us got attacked, then the others would have time to get away. But we’d slowed to a walk, and were now right next to each other.