It turned out that we couldn’t use the tapstones to transmit Morse code. You need two different signals to transmit Morse and it was hard to feel the difference between a dot and a dash. So Varma taught us all a tap code that used two numbers to locate a letter on a grid.

1

2

3

4

5

1

A

B

C/K

D

E

2

F

G

H

I

J

3

L

M

N

O

P

4

Q

R

S

T

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U

5

V

W

X

Y

Z

Each letter was represented by two numbers. Tap once, then a gap, then once again for A. Tap once and then twice for B. Row first then column. It would only work with the modern Latin alphabet so we couldn’t teach it to the locals and we would have to communicate in English and the few other languages that can be easily written using that alphabet.

I didn’t say anything when Varma was teaching us the code but I was sure I’d read about codes like that being used in prisons. Of course knowing a prison code didn’t necessarily mean anything. I’d read about it in a book. Maybe she learned the code in a similar way. I certainly wasn’t going to say anything in front of the others.

###

The rest of the day was taken up with desperate preparations to leave. The Citadel continued to grind slowly down the slope. I added several new roped sections to the cliff face. A team of engineers were still at work building temporary lifts to scale the cliff in sections. The Guild of Navigators had set up a relay of emergency Gondolas to ferry people and supplies up to the plateau.

I was up on the plateau when I heard the first terrifying roar coming from the train station. I ran for the station, convinced that this new sound was the latest crisis to assail the people of Moonstone. Perhaps it was a dragon attack or perhaps the mountain itself had come alive.

It turned out to be the sound of a magical jet engine being tuned.

I know a little about jet engines and slightly less about magical devices. The engine sounded horribly tortured when I heard the first scream of it but by the time I got to the station it sounded pretty smooth.

News that the train engine was running led to a flood of people heading for the train. I joined the existing crew in crowd control until I was called upon to break up a fight on the train.

A few people, Amris amongst them, moved onto the train as soon as the Citadel began to descend. They’d already picked out their berths and stowed their possessions. When the first of the exodus realised that they did not have a free pick of berths some of them got upset. I would have understood if the early starters had claimed more than their fair share of space but none of them had. The problem just seemed to be that the complainers couldn’t have the exact spaces they wanted.

The complainers didn’t want to listen to me when I broke up the argument. So I took a leaf from the Mayor’s book and threatened to have them thrown out of the window, which would put them to the back of the queue.

###

I left my blankets in the second berth in Amris’ compartment and went back to the cliff. I wasn’t ready to say goodbye to the Citadel. I lay down with my head over the edge and watched as the lights of the Citadel moved away from me until, at last, I heard the ground collapse under it, raising a huge cloud of dust and debris.

I realised, as I watched, that I didn’t really believe that the Citadel would move underground. It was the shallowest of the floating islands that made up Moonstone City but it still had to be about a thousand feet from the top of the dome to the bottom of it’s rocky foundations. How was something that deep going to fit into a cavern? And even if it did I couldn’t see how there could possibly be a whole system of caverns that big.

But then I reminded myself that the people who built that thing put a whole city in the sky, and built a magical jet engine, and then managed to conceal how they’d done it from the eyes of history.

Sure enough, as I watched, the lights of the Citadel reached the ground but kept on sinking.

Night fell. I could still see the lights, far below me, but with each passing moment there were fewer of them because the Citadel really was moving away from the hole it had made when it punched into the cavern. I felt a weird stab of envy. What sights might my friends down there be seeing?

When all the lights of the Citadel were gone I walked back to the train.