At this point, two things happen at the same time.

One is that I slice easily through the remaining strands of rope with the dirk.

The other is that, from a little distance away, comes a scream unlike any I have heard before.

I twist round to look. From behind the large rock where we hid, Mola has emerged, naked, in full view of the gathering. Her arms are in the air, her feet wide apart, and she is yelling something at the top of her voice. She looks absolutely inhuman and totally terrifying and whatever she is shouting sounds like a blood-freezing war cry.

The group circling Seb stop immediately and stare in astonishment at the wild, muddy woman now running towards them down the rocky slope.

At the same moment, the mammoth, finally free of its tether, crashes out from the trees. Susan and I dive out of the way and it charges towards the kidnappers, honking and hooting and tossing its head furiously.

The hunters shriek in terror as the angry mammoth thunders across the dusty ground towards its captors. The dogs have fled into the woods. With a flick of the mammoth’s vast head, a tusk sideswipes the lead man and sends him flying through the air to land in a heap a few metres away. The others turn and aim their stone-tipped spears at the bellowing animal, screaming in fright as it charges again.

Between Mola and the mammoth, no one is paying any attention to Seb. Susan and I run round the side of the clearing towards the stake where he is secured. I hear a shout and turn my head. One of the tribesmen has spotted us and starts to run towards us, but is knocked over by a mighty swing of the mammoth’s trunk and sprawls in the dust.

The others have surrounded the animal, and one of them throws a spear, which lodges in its neck, causing it to howl, but it doesn’t stop its rampage.

Susan and I are behind Seb now. I don’t even have time to say hello or ask him how he is. Instead, I start cutting through his wrist-ties, nicking his flesh at the same time in my frenzy and – good old Seb – he doesn’t even complain, though I feel him wince. Seconds later, I’ve cut through.

For a moment, Seb just looks at me, and time seems to stand still. We don’t speak, but we’re sort of talking with our eyes. It’s hard to explain.

And what our eyes say is: You’re annoying, but you’re my brother.

Then I grab Seb by one bloody hand, Susan takes the other and we start to run to the other side of the clearing.

‘Wait!’ says Seb, pulling us sharply to a halt. He wriggles free and runs back to where Kobi is still tied to a stake.

‘We haven’t got time! He’s not even real!’ I scream, but it’s no good. Seb is behind Kobi, frantically cutting through the knotted vine with Kenneth’s dirk.

To my side, I see that Mola has picked up a discarded spear. She holds it in both hands and bares her teeth at the large, hairy man coming towards her, slowly, with a chilling confidence.

‘Mola! Come now!’ Susan cries.

‘No! Run, children, run!’ she shouts.

The big man takes another step and swats aside the spear with a massive hand as easily as if it were a pencil. Mola is defenceless, but stands her ground as the man reaches for her throat with one hand and a stone club with the other, his teeth bared in fury.

Kobi wriggles his hands free from his loosened bonds, smiling his thanks to Seb with a stuck-out tongue before taking the dirk and turning immediately to the one called Erin, beginning to free her in turn. Seb and I start to run, and I am trying so hard to ignore the increasing pain in my croc-bitten leg.

Then Mola is being lifted from the ground by her throat and Susan shouts, ‘Mola!’

At the same time, Mola shouts, ‘Wake up! Wake up!’ and the large man is left clutching at …

Nothing.

Before our astonished eyes, Mola has just vanished from Dreamland. There isn’t time to wonder at this, because the small crowd of Stone Age warriors have decided not to try to fight the mammoth any more, but to run.

And they’re running in our direction.