My parents (all four of them, but particularly Mum) had insisted that the stories were rubbish, and I’d happily believed them. Teachers said it was scaremongering, and that we were being hysterical by believing it. Mr Baxter, my drama teacher, had given us a whole month of lessons themed around doomsday cults and mass hysteria, to give us what he called ‘much-needed perspective’. Everyone had come together to push the view that these rumours were what happened when you allowed anyone to say anything they wanted on the internet anonymously.

My mum – the person I looked to for reassurance above everyone else – had insisted so hard that there was no truth in it that I had been a tiny bit suspicious of what she really thought. She’d called it ‘laughable’ and ‘stupid’. She said science didn’t work like that. She did big laughs out loud to show how ridiculous it was. She agreed that there were lots of things to worry about, but insisted that we weren’t all heading for a mass extinction in the immediate future at least, that if there was something like that on its way, scientists would have sorted it out by now.

She said we should take it as a wake-up call and clean up our act.

Now, of course, she was struggling, but, still, she was trying to be brave. I had chosen to believe her, and Mr Baxter, and everyone else, because it seemed too outlandish even for me to spend too much time worrying about this. It had barely made my top-eleven worries until now. I knew that I would have to scribble over the other ten because this was now the only thing.

I pictured the permafrost. I imagined it thawing out, and a green cloud coming from it and spreading across the planet. There was a reason that that stuff had been locked away, and we had undone it.

I dropped the Twix and grabbed Mum’s hand and gasped for breath. Thinking about it made me panic and fill my lungs with all the air I could, as fast as I could, while it was still there.

She held me and muttered into my hair. ‘Oh, Libby,’ she said, and then she whispered something about violence, but I didn’t stop to ask what she meant. I supposed there would be violence, but I had no capacity to think about that. Not yet.

There was, of course, a caveat, and when Mum found it in the small print she seized upon it. ‘Look!’ she said. ‘It might be all right. They might be able to sort it out.’