As their side wall went up instead of down, it tilted their trench sickeningly, as if to tip them out of it, and Jack realised they were screwed.

They were all going to fall—almost two hundred metres—if not to their deaths, then scattered into the waterfilled maze.

He quickly yelled an order to Alby, then another to Zoe and Lily before—

—a second later, their previously vertical side wall went fully upside down.

If anyone had been there to see it, they would have stared in wonder.

Two hundred metres above the floor of the cavern, Jack and Alby hung from their upside-down trench—one-handed, by the fingertips of their titanium artificial left hands—with Zoe and Lily dangling from their waists.

At Jack’s command, Jack and Alby had used their titanium fists to quickly punch shallow fingerholds into the stone wall of their trench, deep enough to get a grip.

And then Zoe had grabbed onto Jack’s waist and Lily had clutched onto Alby’s.

And so, as the trench came fully upside down, they hung there, dangling high above the maze, their feet swinging, waiting for the next rotation.

It was a feat no person with regular hands could do.

But Jack and Alby’s titanium fingers weren’t regular. In addition to being superhard, thanks to their mechanical servos, they were also superstrong, and they clamped onto their fingerholds with vice-like intensity until a few minutes later when, with a great groaning, the maze turned once more and their roof became a wall again and they all tumbled onto the side-wall of the trench, itself now a shelf once more.

They then hustled for the next blockhouse, dived into it, and, safe once again, gasped for air.

Alby turned to Jack, raising his titanium left hand. It was, after all, Jack’s old one which he’d given to Alby after the incident with Jaeger Eins and Dion and the filament weapon.

‘This thing is awesome,’ Alby said. ‘Best second-hand hand in the world.’

‘Better believe it,’ Jack said. ‘When Wizard built it for me twenty years ago, he promised it would be better than the hand I was born with. Turns out, it is.’

During that break, Lily figured out the rotation sequence.

‘Oh, I see it now.’ She gestured at the original symbol.

‘This image represents the sequence of rotations, but it’s tricky. The angles between the lines represent the direction of each rotation: see how some go to the left and some go right. But the length of each line shows the duration between each rotation: see how some are longer than others. That’s how we got caught.’

Jack said, ‘It looks like you got it figured out now. I’m so glad you guys caught up with me. There’s literally no way I could have made it through this thing without you.’

Onward they went, through the long, rotating maze.