From the gloom of the guard’s van behind him someone coughed, pointedly. Vimes emerged with a little smile and said, ‘Plausible deniability, eh, Mister Lipwig? But well done, anyway. Just between ourselves: those golems that’ll never be used … What do you suppose they’re doing right now?’

Moist opened his mouth to deny all knowledge of the golems, then thought better of it. Something in Vimes’s eyes dared him to try. ‘Digging their way back home, I trust,’ he said. ‘Rather more easily since they tunnelled their way up here in the first place.’

And in the distance behind the train, the rickety bridge was falling bit by bit into the valley in a curious kind of mechanical ballet. It would be some time before it could be used again, thought Moist – but now we’ve got Rhys this far we can throw everything into getting this damn bridge built properly.

And a few hours later, as the golems tunnelled under his tavern, the Grosszügig Stein, Herr Muckenfuss noticed the floor dancing and every glass and stein in the building shook rapidly. Plump though he was, he scooped up every falling stein and glass with great determination until there was a sudden settling in the air and the tavern was eerily silent. He looked at Herr Bummel, his solitary customer, who stared at the dregs in his stein of the new cask of Old Blonk they had been sampling before whispering in impressed tones, ‘I think I’ll have the same again.’

As Bonk came ever closer and the horizon was now eaten by the mountains – looming outlines visible against the night sky, steep slopes occasionally catching the moonlight – Commander Vimes called a council of war in the guard’s van, the centre of operations. With the experience of the attacks at the Paps and the destruction of the Flyer to draw upon, careful plans were laid for the defence of the train and the King.

‘Well now, look around, all of you. What you see is canyons and trees. If I was a grag I’d probably see this next stretch as my last available opportunity to derail Iron Girder.’

Vimes’s face was grim as he outlined his proposals and Rhys nodded his approval, interrupting now and then to add a refinement.

‘We must also take care of attacks from above,’ the commander continued. ‘As we’ve seen, Iron Girder is well protected. She has her corsets on now, thanks to Dick’s new alloy, but we might have to fight on top of the carriages. I see you grin, Mister Lipwig. So, smart boy, if that happens I invite you to join me and the others on the roof when the time comes. Are you game, sir? It’s likely to be very dangerous up there.’

The inner Moist patted himself on the back as he thought of his illicit adventure on top of the Flyer. He could dance on the train, jump and spin and twirl, because he had the measure of the moods of every part of the train.