‘Ah, Commander Vimes,’ said the King to Vimes, who had arrived at speed. ‘You should know about the dark-accustomed eye if any human does. There’s a long straight ahead and Dick hadn’t seen the derailment, but I did, just in time. Now, there may be injured people up there.’

And then the King was running towards the flames, adopting the traditional dwarf strategy of running at the enemy with as much weaponry as you could swing. But Vimes caught up with him and rolled him to the ground just as an explosion rattled the trees and bounced off the mountains. The Flyer’s boiler had blown up. Ahead of them now was just a warm mist and the occasional clink of stricken metal.

Vimes got the King upright and said, ‘Apologies for the lèse-majesté – though you must know that we Vimeses have gone a lot further than that in the past. You should have listened. The whole deal for the crew of the decoy Flyer was to run away as fast as possible if attacked, but not before making sure that the emergency bung in the boiler was strapped right down.’

‘Ah, yes, Blackboard Monitor, how easily we revert to type in an emergency. I’m sorry to have put you to extra trouble.’

‘That’ll teach the buggers a lesson,’ said Dick, panting as he caught up with them. ‘They’ll think twice about messing with one of my engines again.’

The crew of the Flyer were up a little gully, into which they had dived for shelter. It had once been home to frogs. Regrettably, it still was, and several of the designated bodyguards rose from the little swamp with nothing more than torn clothing and a lot of mud, some of which was hopping, but Cheery Littlebottom was as cheery as her name suggested.

There seemed to be no grags, but even as Moist looked around, an arm dropped out of a tree, still holding a club in an iron grip. And hereabouts, if you cared to look, and frankly nobody cared to do so but did nonetheless, there were several signs that grags and delvers and many others of the dark underworld had passed away in this spot, resting at peace and, thanks to the exploding boiler, in pieces.

Detritus appeared out of the gloom, saying, ‘One or two of dem was still out dere. Not any more.’ He slammed down a breastplate with a resounding clang.

‘You all right, lads?’ said Simnel to the engineers. ‘Shame about the Flyer. It hurts, killing a locomotive, and it means we’ve not got either a pathfinder or a back-up engine no more. We need to clear the track now, then we’ll pick up the scrap when we come back, to go towards a new Flyer. After all, we’re getting reet good at building these things. But any bits of micromail you find, like this here’ – he pointed at the arm holding the axe – ‘I’ll have now, mind, call it tit for tat. It’ll be another trophy for Iron Girder.’