I can’t stop to think.

‘Come on!’ I tell the others, and push a squealing Tammy through the gap first.

I’m not going to make it.

‘Go!’ I yell to Iggy, and he too is through, as I see the rip in the force field mending itself from the top.

I barely notice the loud creaking noise beside me as another tree succumbs to the fire and begins to topple. I have about a second left and hurl myself at the hole, but I’m held back.

Dark Streak is on me, her thin, strong hand grabbing the collar of my jumper.

She growls something in my ear and as I try to wriggle from her grasp I see her hideous, burnt face and smell the blackened hair.

I did my best, I think, and prepare to give in, when the falling tree connects with her back and sends us both sprawling.

There is a gap left at the bottom of the hole that’s about thirty centimetres high, and I scramble towards it and roll under. My leg is out last and I feel a searing pain shoot through my foot as the force field closes around it …

But I’m free.

Panting and choking, I get up on my elbows and see Dark Streak, immobile beneath the burning tree, her blackened and burnt face in a deathly grin of agony that will – it turns out – haunt my dreams for years to come.

Iggy is on all fours, retching and coughing, while a blackened Suzy pecks at the ground next to him. Tammy is bent over, hands on the knees of her filthy jeans, panting, while the spaceship hovers a few metres away waiting for us.

Beside me lies Hellyann. I think she is motionless, and then I notice a slight rising and falling of her chest and I scramble over to her.

‘Hellyann. Hellyann!’ I say in her ear and her eyes flicker open. ‘Can you hear me?’

She blinks in response.

I’m blinking myself to try to clear my eyes of tears. ‘Why?’ I ask. ‘Why did you do that?’

‘I dit not understant, when I wass young,’ she says. Her voice is very quiet and it’s not clear if she’s speaking to me, or to herself. ‘But now I do. It iss a case of thinking that someone else iss more important than yourself.’

‘What?’ I say.

‘Sacrifice. It iss not rational. Humans are not always rational. That iss the point.’ She looks at me, and then to Iggy, who has crawled over. ‘Thank you,’ she says. ‘For being my friends.’

Her eyes are closing. Then her arm twitches. She squints with the effort of moving it as she brings her hand over her heart and touches it with three fingers. Then her eyes shut and this time I know it is forever.

‘Hey, kids! Get in. Quickly! The perimeter patrol will be around in a few seconds.’

I have never been so relieved to hear a bot’s voice.

The spacecraft hovers alongside us, and we cram together. My foot is badly burnt from the force field and I can’t put any weight on it. None of us says a word all the way back. No one pursues us from Earth Zone, although there are a lot of aerial vehicles heading in the other direction, towards the growing plume of smoke billowing into the white sky.

Tammy sits next to me, staring straight ahead and holding my hand – the unburnt one – so hard there will be a bruise there tomorrow.

Iggy is curled up, hugging Suzy.

I don’t want to say anything.

We all realise that there is only one thing to say and that is:

How are we getting back to Earth?

Obviously we want to know how, but as long as we don’t know, then we can close our eyes and pretend that everything is all right. So that is what I do for a few minutes. I close my eyes and imagine that I’m in the school taxi-bus, with Tammy next to me, and Iggy showing me his Death Ray …

It’s double history first thing, which is not my favourite, but then we have art with Miss Khan, who is OK, and the theme is space travel and I have an awesome idea for drawing an alien city …

This is nice, I think. So long as I don’t open my eyes, this is great.

And then I do open my eyes, and wish I hadn’t.