He screws up his eyes, concentrating; squinting at me, as if he’s trying to see through a dirty window. ‘Rust-me?’ He teeters, unsteady still on his feet.

‘Yes. Trust me.’ I hold out my hand towards him, beckoning for him to take it.

The sky is so black now it feels like night is falling, and the rain’s properly splattering too. ‘Come on! Hurry up!’

The boy takes another staggery step away from me, blinking suspiciously. Thunder booms. The storm’s coming in really fast, it’ll reach us soon.

Then I have an idea. I know what’ll help him trust me. I roll the spear towards him along the ground. The boy snatches up his spear, and glares at me. Trickles of blood-tinged rain are running down the sides of his face and his hair is stuck to his cheek. The boy’s eyes narrow. Lightning lights us up, jittery and awful, and the spear in the boy’s hand flashes bone white. Thunder crashes and bangs almost overhead. Suddenly, I realise that I might have just made a huge mistake. What was I thinking? This boy’s not my friend; I’ve no idea who he is or what’s happened to him … or what he might do next.

‘I trust you,’ I say, but my voice has gone all squeaky and unconvincing.

Lightning flashes in a huge zigzag across the black sky.

Thunder crashes like the world is breaking. The boy stares at me, his eyelids flickering. He can’t pass out again; not here, not now.

‘Please!’ I say, and our eyes lock.

He rams his spear into the sand and leans on it like a walking stick. ‘Peas,’ he says solemnly, and he starts to stumble towards me. ‘I come kayyfff!’

I laugh. A mad, scared, electric laugh. ‘Hurry up then,’ I say in relief, ‘before we both get frazzled.’

I go to the boy and hold out my hand to help him; he doesn’t take it, but he does hobble closer to my side, still leaning on his spear, so that when, in a new touch of dizziness, he starts to sway I can put my arm out to steady him.

‘Just hold on to me!’ I have to shout over another crash of thunder.

He puts his heavy hand on my shoulder. He grips it so tight I almost wince; his fingers feel like claws. And that’s how, together, we cross the river through the pelting rain: me, Charlie Merriam, and him, this wild, unpredictable boy.

We step off the last stepping stone and our feet squelch down into the ooze of mud. The boy drops his hold of me and leans back on to a tree trunk. I lean next to him, and we stand still a moment, both of us breathing hard. The air tastes sharp and electric, full of storm shivers. I sense the boy looking at me. I peek at him out of the corner of my eye too and a little tingle zigzags through my bones. Thunder booms.