'That's not necessarily a good thing,' said Moist. 'How do you know her?'

'We used to work with her brother,' said Mad Al. 'On the Mark 2 tower.' Moist listened. It was a whole new world. Sane Alex and Mad Al were old men in the clacks business; they'd been in it for almost four years. Then the consortium had taken over, and they'd been fired from the Grand Trunk on the same day that Undecided Adrian had been fired from the Alchemists' Guild chimney, in their case because they'd spoken their mind about the new management and in his case because he hadn't moved fast enough when the beaker started to bubble. They'd all ended up working on the Second Trunk. They'd even put money into it. So had others. It had all kinds of improvements, it would be cheaper to run, it was the bee's knees, mutt's nuts and various wonderful bits of half a dozen other creatures. And then John Dearheart, who always used a safety lanyard, landed in the cabbage field and that was the end of the Second Trunk. Since then, the trio had done the kinds of jobs available to new square pegs in a world of old round holes, but every night, high above, the clacks flashed its messages. It was so close, so inviting, so . . . accessible. Everyone knew, in some vague, half-understood way, that the Grand Trunk had been stolen in all but name. It belonged to the enemy.

So they'd started an informal little company of their own, which used the Grand Trunk without the Grand Trunk's knowing. It was a little like stealing. It was exactly like stealing. It was, in fact, stealing. But there was no law against it because no one knew the crime existed, so is it really stealing if what's stolen isn't missed? And is it stealing if you're stealing from thieves? Anyway, all property is theft, except mine. 'So now you're, what was it again . . . crackers?' Moist said. 'That's right,' said Mad Al. 'Because we can crack the system.'

'That sounds a bit over-dramatic when you're just doing it with lamps, doesn't it?'

'Yes, but “flashers” was already taken,' said Sane Alex. 'All right, but why “Smoking Gnu”?' said Moist. 'That's cracker slang for a very fast message sent throughout the system,' said Sane Alex proudly. Moist pondered this. 'That makes sense,' he said. 'If I was a team of three people, who all had a first name beginning with the same letter, that's just the kind of name I'd choose.' They'd found a way into the semaphore system, and it was this: at night, all clacks towers were invisible. Only the lights showed. Unless you had a good sense of direction, the only way you could identify who the message was coming from was by its code. Engineers knew lots of codes. Ooh, lots. 'You can send messages free?' said Moist. 'And nobody notices?' There were three smug smiles. 'It's easy,' said Mad Al, 'when you know how.'

'How did you know that tower was going to break down?'

'We broke it,' said Sane Alex. 'Broke the differential drum. They take hours to sort out because the operators have to—' Moist missed the rest of the sentence. Innocent words swirled in it like debris caught in a flood, occasionally bobbing to the surface and waving desperately before being pulled under again. He caught 'the' several times before it drowned, and even 'disconnect' and 'gear chain', but the roaring, technical polysyllables rose and engulfed them all. '—and that takes at least half a day,' Sane Alex finished. Moist looked helplessly at the other two. 'And that means what, exactly?' he said. 'If you send the right kind of message you can bust the machinery,' said Mad Al. 'The whole Trunk?'

'In theory,' said Mad Al, 'because an execute and terminate code—' Moist relaxed as the tide came back in. He wasn't interested in machinery; he thought of a spanner as something which had another person holding it. It was best just to smile and wait. That was the thing about artificers: they loved explaining. You just had to wait until they reached your level of understanding, even if it meant that they had to lie down. '—can't do that any more in any case, because we've heard they're changing the—' Moist stared at the pigeon for a while, until silence came back. Ah. Mad Al had finished, and by the looks of things it hadn't been on a high note. 'You can't do it, then,' said Moist, his heart sinking. 'Not now. Old Mr Pony might be a bit of an old woman but he sits and niggles at problems. He's been changing all the codes all day! We've heard from one of our mates that every signaller will have to have a personal code now. They're being very careful. I know Miss Adora Belle thought we could help you, but that bastard Gilt has locked things up tight. He's worried you're going to win.'

'Hah!' said Moist. “We'll come up with some other way in a week or two,' said Undecided Adrian. 'Can't you put

it off until then?'

'No, I don't think so.'

'Sorry,' said Undecided Adrian. He was playing idly with a small glass tube, full of red light. When he turned it over, it filled with yellow light. 'What's that?' Moist asked. 'A prototype,' said Undecided Adrian. 'It could have made the Trunk almost three times faster at night. It uses perpendicular molecules. But the Trunk's just not open to new ideas.'

'Probably because they explode when dropped?' said Sane Alex. 'Not always.'

'I think I could do with some fresh air,' said Moist. They stepped out into the night. In the middle distance the terminal tower still winked, and towers were alight here and there in other parts of the city. 'What's that one?' he said, like a man pointing to a constellation. 'Thieves' Guild,' said Undecided Adrian. 'General signals for the members. I can't read 'em.'

'And that one? Isn't that the first tower on the way to Sto Lat?'

'No, it's the Watch station on the Hubwards Gate. General signals to Pseudopolis Yard.'

'It looks a long way off.'

'They use small shutter boxes, that's all. You can't see Tower 2 from here - the University's in the way.' Moist stared, hypnotized, at the lights. 'I wondered why that old stone tower on the way to Sto Lat wasn't used when the Trunk was built? It's in the right place.'

'The old wizard tower? Robert Dearheart used it for his first experiments, but it's a bit too far and the walls aren't safe and if you stay in there for more than a day at a time you go mad. It's all the old spells that got into the stones.' There was silence and then they heard Moist say, in a slightly strangled voice: 'If you could get on to the Grand Trunk tomorrow, is there anything you could do to slow it down?'

'Yes, but we can't,' said Undecided Adrian. 'Yes, but if you could?'

'Well, there's something we've been thinking about,' said Mad Al. 'It's very crude.'

'Will it knock out a tower?' said Moist. 'Should we be telling him about this?' said Sane Alex. 'Have you ever met anyone else that Killer had a good word for?' said Mad Al. 'In theory it could knock out every tower, Mr Lipwig.'

'Are you insane as well as mad?' said Sane Alex. 'He's government!'

'Every tower on the Trunk?' said Moist. 'Yep. In one go,' said Mad Al. 'It's pretty crude.'

'Really every tower?' said Moist again. 'Maybe not every tower, if they catch on,' Mad Al admitted, as if less than wholesale destruction was something to be mildly ashamed of. 'But plenty. Even if they cheat and carry it to the next tower on horseback. We call it . . . the Woodpecker'. 'The woodpecker?'

'No, not like that. You need, sort of, more of a pause for effect, like . . . the Woodpecker! '. . . the Woodpecker,' said Moist, more slowly. 'You've got it. But we can't get it on to the Trunk. They're on to us'

'Supposing I could get it on to the Trunk?' said Moist, staring at the lights. The towers themselves were quite invisible now. 'You? What do you know about clacks codes?' said Undecided Adrian. 'I treasure my ignorance,' said Moist. 'But I know about people. You think about being cunning with codes. I just think about what people see—' They listened. They argued. They resorted to mathematics, while words sailed through the night above them. And Sane Alex said: 'All right, all right. Technically it could work, but the Trunk people would have to be stupid to let it happen.'

'But they'll be thinking about codes,' said Moist. 'And I'm good at making people stupid. It's my job.'

'I thought your job was postmaster,' said Undecided Adrian. 'Oh, yes. Then it's my vocation.' The Smoking Gnu looked at one another. 'It's a totally mad idea,' said Mad Al, grinning. 'I'm glad you like it,' said Moist. There are times when you just have to miss a night's sleep. But Ankh-Morpork never slept; the city never did more than doze, and would wake up around 3 a.m. for a glass of water. You could buy anything in the middle of the night. Timber? No problem. Moist wondered whether there were vampire carpenters, quietly making vampire chairs. Canvas? There was bound to be someone in the city who'd wake up in the wee small hours for a wee and think, 'What I could really do with right now is one thousand square yards of medium grade canvas!' and, down by the docks, there were chandlers open to deal with the rush. There was a steady drizzle when they left for the tower. Moist drove the cart, with the others sitting on the load behind him and bickering over trigonometry. Moist tried not to listen; he got lost when maths started to get silly. Killing the Grand Trunk . . . Oh, the towers would be left standing, but it would take months to repair them all. It'd bring the company down. No one would get hurt, the Gnu said. They meant the men in the towers. The Trunk had become a monster, eating people. Bringing it down was a beguiling idea. The Gnu were full of ideas for what could replace it - faster, cheaper, easier, streamlined, using imps specially bred for the job . . . But something irked Moist. Gilt had been right, damn him. If you wanted to get a message five hundred miles very, very fast, the Trunk was the way to do it. If you wanted to wrap it in a ribbon, you needed the Post Office. He liked the Gnu. They thought in a refreshingly different way; whatever curse hung around the stones of the old tower surely couldn't affect minds like theirs, because they were inoculated against madness by being a little bit crazy all the time. The clacks signallers, all along the Trunk, were . . . a different kind of people. They didn't just do their job, they lived it. But Moist kept thinking of all the bad things that could happen without the semaphore. Oh, they used to happen before the semaphore, of course, but that wasn't the same thing at all. He left them sawing and hammering in the stone tower, and headed back to the city, deep in thought.

Chapter Thirteen

The Edge of the Envelope In which we learn the Theory of Baize-Space — Devious Collabone - The Grand Trunk Burns — So Sharp You'll Cut Yourself— Finding Miss Dearheart - A Theory of Disguise - Igor Moveth On - 'Let This Moment Never End' - A Brush with the Trunk - The big sail unfurls - The Message is Received Mustrum Ridcully, Archchancellor of Unseen University, levelled his cue and took careful aim. The white ball hit a red ball, which rolled gently into a pocket. This was harder than it looked because more than half of the snooker table served as the Archchancellor's filing system,* and indeed to get to the hole the ball had to pass through several piles of paperwork, a tankard, a skull with a dribbly candle on it and a lot of pipe ash. It did so. * Ridcully practised the First Available Surface method of filing. 'Well done, Mr Stibbons,' said Ridcully. 'I call it baize-space,' said Ponder Stibbons proudly. Every organization needs at least one person who knows what's going on and why it's happening and who's doing it, and at UU this role was filled by Stibbons, who often wished it wasn't. Right now he was present in his position as Head of Inadvisably Applied Magic, and his long-term purpose was to see that his department's budget went through on the nod. To this end, therefore, a bundle of thick pipes led from under the heavy old billiard table, out through a hole in the wall and across the lawn into the High Energy Magic building, where - he sighed - this little trick was taking up 40 per cent of the rune-time of Hex, the University's thinking engine. 'Good name,' said Ridcully, lining up another shot. 'As in phase-space?' said Ponder, hopefully. 'When a ball is just about to encounter an obstacle that is not another ball, you see, Hex moves it into a theoretical parallel dimension where there is unoccupied flat surface and maintains speed and drag until it can be brought back to this one. It really is a most difficult and intricate piece of unreal-time spell casting—'