‘No tanks!’ he chortles, like I’m the best joke ever. And his big snort of laughter makes me giggle even more. My sides start to hurt. I lean on the cool rock, looking out, trying to stop laughing.

Even though the rain has stopped, everywhere’s still dripping. I breathe a big gulp of fresh-washed air, steadying myself; for a moment it’s so quiet I can hear the gurgle of all the little brown rivulets of rainwater trickling down the sheer rock. I peek back at the boy; he peeks at me too and we both erupt into giggles again. I don’t think either of us even knows any more what we’re laughing about. But it doesn’t matter. ‘Come on!’ I say, through my giggles. ‘Let’s get down from here before we fall and break our necks.’

Harby shakes his head, a vague smile still on his lips. ‘Who you, Cholliemurrum?’ he says, peering at me curiously like I’m a specimen in a museum. ‘Why you come here?’

Suddenly I see myself through his eyes. If I think he looks odd, he must think I look a thousand times odder! I mean, I’ve done a whole topic at school on the Stone Age. But he’s never even imagined a somebody like me – I glance down at my bloody knee, my muddy trainers, my raggedy blue T-shirt. ‘Cholliemurrum,’ I murmur in his gravelly voice, and a mad little laugh slips out. I barely recognise myself. ‘Why did I come here?’ I say to the boy. ‘I honestly have no idea.’

He looks utterly confused. ‘No eye deer?’ he echoes, pointing at the painting of the deer just visible through the cave mouth. I giggle, but then I think about all the other wild creatures in the cave paintings and my laugh pops like a bubble.

I look at Harby. He’s suddenly serious; every trace of dancing, twinkling laughter has drained from his eyes, which are staring hard at me.

‘What?’ I say.

Holding my gaze, he grabs my wrist, tight like an eagle claw.

‘Oi!’ I say, squirming to take my hand away.

But he ignores me. ‘I know why you come here, Cholliemurrum,’ he whispers, tickly close in my ear.

‘Why?’ I blink at him.

He presses my palm to the handprint wall, right on top of the smallest, freshest handprint of them all.

‘You come help me find my sister!’ says Harby triumphantly, letting go of my hand.

I peel my palm away and gaze at the tiny handprint; something twangs, painful and hollow, deep down inside me.

‘Mothga,’ I murmur.

Then suddenly my heart flurries. ‘Mothga!’ I grab Harby’s wrist, tight like he grabbed mine. ‘Mothga! Yes! Harby, I think you’re right! I think I do know where your sister is.’ My words come tumbling out, all in a rush.

Harby cocks his head on one side, screws up his eyes, like he hasn’t understood.

‘Mothga,’ I say. ‘In there.’ I point at the cave depths.

He stares at me, eyebrows raised in stunned surprise. ‘Mothga?’ he says, shaking his head slowly. ‘In wolf kayff?’