‘Oh … You don’t remember … do you?’ I say softly, and then I get why he’s so odd and confused and frightened. He’s lost his memory. ‘Don’t worry, you banged your head, that’s all.’ I touch my own head in the place where his cut is.

As if he’s only just noticed it he reaches up and feels the dark oozy gash across his forehead. ‘Yoooo make this?’ he says in horror, looking down at his bloody fingertips, staggering backwards.

‘No! No! Of course I didn’t. I just found you. I found you in the water and I …’

I hesitate, what just happened catching up with me suddenly. ‘… I … I saved you … I think …’ I don’t quite believe it myself; I’ve never saved anyone before. I smile at the boy, dazed, proud almost.

He doesn’t smile back, instead he ignores me; he’s fiddling with one of the twisted string bracelets on his wrist. ‘Mothga …’ he murmurs, stroking the bracelet tenderly. ‘I member Mothga …’ His eyes flick back to me, fast and accusing. ‘Where Mothga? You take Mothga, Cholliemurrum?’

I shake my head. ‘No. I don’t know what you’re on about. What’s Mothga? ‘

The boy gazes sadly at the string bracelet. ‘Mothga my sister. Mothga my baby sister.’

‘Baby sister,’ I echo softly. My heart pangs and a strange ache pulls at the pit of my stomach.

I see a sudden cloud of remembering cross the boy’s eyes. ‘Mothga!’ he shouts, looking all about in a panic. ‘Where Mothga? Mothga all alone! I need make safe! Fast! Fast!’

Before I can say or do anything, he leaps to his feet and instantly his face turns ghost pale; his eyes roll back and he collapses in a heap again like he’s melted.

I run over to him. He’s OK, he’s breathing thickly; he just fainted I think. I stare at his blood-streaked, sandy face. What’s wrong with him?

A memory pings into my head.

Concussion? I think to myself, from when he bashed his head on the rock. Beaky had concussion once, when she fell off the climbing frame in primary school. She called it conk-cushion afterwards, when she was better. But it wasn’t even slightly funny at the time. She was properly knocked out and she just lay there in the playzone, really still and pale so we knew she wasn’t pretending. Then when she woke up she didn’t know Lamont or me at all; she just stared at us like we were strangers. I remember how she screamed and shouted Go away! at us. That was the scariest part. She didn’t even know who we were or who she was or anything. Mrs Rodriguez had to call an ambulance.

An ambulance! That’s what I need. If only Mum and Dad had got me a phone then it’d be easy. I scan up and down the river for Beaky, Lamont … anyone … but there’s still nobody.

‘OK,’ I say to the boy, whether he can hear me or not. ‘I’m going to get help.’ I straighten Dad’s backpack on my shoulders, then I scramble on to the ridge and run towards the path back up through the forest to the hospital.