The evening before they were to leave Bonk, Moist wandered down to the railhead, idly pondering recent events. Well, he thought, the world has seen the footplate of Iron Girder and the Queen has been given her crown back and according to Commander Vimes the worst of the grags are either dead or behind bars.

At the makeshift station Iron Girder was being guarded by Nobby Nobbs and Fred Colon, who were both sound asleep. Iron Girder, however, wasn’t, although the kettle was barely simmering after a long day giving rides to the locals up and down the single track.

Moist tiptoed to the empty footplate and whispered, ‘What are you, Iron Girder?’ There was a moment of silence, then a shimmer as the wisps of steam drifted up into the night air above the locomotive and a voice breathed into his brain, soft and warm and somehow damp.

‘My, oh my, Mister Lipwig, you are the smart one, just as they say. I am me. I am Iron Girder. But all it takes is for people to believe and I am no longer just an artefact put together by clever engineers. I am an idea, a something made of nothing, whose time has come to be. Some even call me “goddess”.’

Moist’s fleeting thought about traditional representations of goddesses in diaphanous nighties with maybe an urn or two was banished as the voice continued a little more sharply.

‘Am I not beautiful? And I tell you, my children will be even better! More sleek and more handsome and more powerful! Even now Mister Simnel is making my children for me. In time I will become ubiquitous, part of the landscape which is ennobled by my fleeting passage. I hear the worship every day that tells me that I am power personified and those who think to oppose me and put out my fire will find themselves thwarted, and swiftly. I, Mister Lipwig, I will rule on the up line and I will rule on the down line.’

In the twilight Moist saw a skinny figure walk up to Iron Girder. Dick Simnel shut down some hissing mechanism or other and the voice, the beautiful voice, was silenced.

‘Aye, she’s gradely all right! Come to see her for the last time before we head back to the city, have you? I can’t blame you. Everyone’s been wanting to see ’er, and I won’t lie, Mister Lipwig, it’s a wrench to leave her behind, for all she’s got good work to do ’ere. Iron Girder, she’s turned out to be a great lass. She was the power and she was ’arnessed, by gum. Oh, yes! ’arnessed by the sine and the cosine, and even the tangent had its little ’and in there somewhere! But not least she was tamed by my sliding rule.’

Dick grinned at Moist and continued. ‘People see Iron Girder and they’re gobsmacked by what can be done with mathematics! Don’t you go thinking she’ll burn you with living steam because she won’t. I’ve seen to it that she won’t. She’ll always be my favourite engine, Mister Lipwig, the queen of them all. She lives. How could anyone say she doesn’t?’