Finn uncaps the bottle and has a swig. ‘So the ghost nun,’ he says. ‘Do you believe in stuff like that?’

‘Yeah, I do,’ Julia says. ‘Some of it. Maybe not the ghost nun – I bet the teachers just made her up to stop us doing this – but some stuff. How about you?’

Finn takes another swig. ‘I don’t know,’ he says. ‘I mean, no, because there’s no scientific evidence, but I actually think I’m probably wrong. You know?’

‘More rum,’ Julia says, holding out her free hand. ‘I think I need to catch up.’

Finn passes it over. ‘Like, OK: everyone in history’s thought they were the ones who finally knew everything. In the Renaissance, right, they were positive they knew exactly how the universe worked, till the next set of guys came along and proved that they were missing like a hundred important things. And then that set of guys were sure they had it all down, till another set came along and showed them parts they were missing.’

He glances at Julia, checking if she’s laughing at him, which she isn’t, and if she’s listening. Which she is, completely.

‘So,’ he says, ‘it’s pretty unlikely, just mathematically, that we’re living in the one single era that happens to finally have everything figured out. Which means there’s a decent possibility that the reason we can’t explain how ghosts and stuff could exist is because we haven’t figured it out yet, not because they don’t. And it’s pretty arrogant of us to think it definitely has to be the other way round.’

Finn takes a drag of his cigarette and squints at the blow of smoke like it’s turned fascinating. Even in the moonlight, Julia can see the deeper colour on his cheeks.

‘Well,’ he says. ‘Probably that all sounded totally stupid. You can tell me to shut up now.’

Julia notices something that she never had room to spot before, through the whirl of Does he fancy me do I fancy him is he going to try would I let him how much would I let him. She really likes Finn.

‘Actually,’ she says, ‘since you mentioned it, it’s one of the least stupid things I’ve heard in ages.’

He gives her a quick sideways glance. ‘Yeah?’

Julia would love with all her heart to show him. Lift her hand, send the Lucozade bottle slowly rising through the rich moonlight. Upend it, set the falling droplets of rum spiralling like a tiny amber galaxy against the star-thick sky. See the slow sheer joy lighting his face right through. The thought of what would happen to her makes the back of her neck twitch.

‘OK,’ she says. ‘Here’s something I’ve never told anyone.’

Finn turns his head to look at her properly.