He strapped the BC across Forest’s back.

Mackenzie tried to argue, but Ahab raised his voice. ‘Enough, Mackenzie.’ He grabbed Forest by the collar and pulled his face close. ‘Forest, listen to me. You’ll need to kick . . . really kick. Like your life depends on it.’

‘I have something to tell you, Ahab. It’s important!’ said Forest.

‘There’s no time,’ said Ahab roughly. ‘Don’t argue with me.’

The singing-drone was louder than ever – a huge wave was forcing itself up the tunnel. Ahab and Mackenzie gripped each other’s arms, keeping Forest in between them. When the wave came, it came with such force it ripped Ahab’s headtorch from his head, swirling it away into the water.

When the water levelled out, Ahab yanked his fins off and helped Forest into them. They were too big, but he pulled the straps as tight as they could go. That was the last of his gear.

‘Well,’ said Ahab, a sorrowful smile on his face. ‘I suppose this is goodbye.’ Even the drone had dimmed, as though honouring their farewell.

This couldn’t be happening.

I can’t let Ahab die in here!

Mackenzie unclasped his gold chain – it still hung around his neck – and handed it to Ahab. ‘Take this!’

Ahab grabbed the chain, exasperated. ‘Mackenzie . . .’

But Mackenzie didn’t let go of his end of the chain. ‘You said I was a man! You said when I brought this chain back from the bottom of the sea, I was a man! You were both there when that happened!’

‘Mackenzie, this really isn’t the time —’

‘This is exactly the time!’ roared Mackenzie. He clasped the chain around Ahab’s neck. ‘I’m not gonna let this cave, my brother, my mum, the whole damn ocean, take anything from me ever again! It doesn’t matter if you don’t have a mask. You don’t need one. You just follow me – I’ll get us out of here.’ He yanked at his spare regulator, also attached to his oxygen tank, and shoved it into Ahab’s mouth. ‘Because I’m not losing that gold chain ever again!’ He pounded Ahab’s shoulder. ‘Keep your eyes closed, and trust me!’

Mackenzie pushed Forest, Ahab and himself into the water. He guided Ahab’s hands to the side of his BC, looped the rope around him, and then Mackenzie – with powerful kicks – set off into the tunnel, holding on to Forest to guide him and dragging Ahab behind.

CHAPTER 57

AHAB

Ahab clung to his cousin and kicked as best he could as they fought their way out of the tunnel. He kept his eyes shut against the rushing water. The rope cut into his side, the regulator in his mouth the only safe thing in this terrifying world, reduced to the tiny space around him.