'I thought you didn't like books,' said Agnes. 'I don't,' said Granny, turning a page. 'They can look you right in the face and still lie. How many fiddle players are there in the band?'

'I think there are nine violinists in the orchestra.' The correction appeared to pass unnoticed. 'Well, there's a thing,' said Granny, without moving her head. 'Seems that twelve of 'em are drawing wages, but three of 'em is over the page, so you mightn't notice.' She looked up and rubbed her hands happily. 'Unless you've got a good memory, that is.' She ran a skinny finger down another erratic column. 'What's a flying ratchet?'

'I don't know!'

'Says here “Repairs to flying ratchet, new springs for rotation cog assembly, and making good. Hundred and sixty dollars and sixty-three pence.” Hah!' She licked her finger and tried another page - 'Even Nanny ain't this bad at numbers,' she said. 'To be this bad at numbers you've got to be good. Hah! No wonder this place never makes any money. You might as well try to fill a sieve.' Agnes darted into the room. 'There's someone coming!' Granny got up and blew out the lamp. 'You get behind the curtains,' she commanded. 'What're you going to do?'

'Oh. . . I'll just have to make myself inconspicuous. . .' Agnes hurried across to the big window and turned to look at Granny, who was standing by the fireplace. The old witch faded. She didn't disappear. She merely slid into the background. An arm gradually became part of the mantelpiece. A fold of her dress was a piece of shadow. An elbow became the top of the chair behind her. Her face became one with a vase of faded flowers. She was still there, like the old woman in the puzzle picture they sometimes printed in the Almanack, where you could see the old woman or the young girl but not both at once, because one was made of the shadows of the other. Granny Weatherwax was standing by the fireplace, but you could see her only if you knew she was there. Agnes blinked. And there were just the shadows, the chair and the fire. The door opened. She ducked behind the curtains, feeling as conspicuous as a strawberry in a stew, certain that the sound of her heart would give her away. The door shut, carefully, with barely a click. Footsteps crossed the floor. A wooden scraping noise might have been a chair being moved slightly. A scratch and a hiss were the sound of a match, striking. A clink was the glass of the lamp, being lifted. . . All noise ceased. Agnes crouched, every muscle suddenly screaming with the strain. The lamp hadn't been lit-she'd have seen the light around the curtain. Someone out there was making no noise. Someone out there was suddenly suspicious. A floorboard squeaked verrrry slowwwly, as someone shifted their weight. She felt as if she was going to scream, or burst with the effort of silence. The handle of the window behind her, a mere point of pressure a moment ago, was trying seriously to become part of her life. Her mouth was so dry that she knew it'd creak like a hinge if she dared to swallow. It couldn't be anyone who had a right to be here. People who had a right to be in places walked around noisily. The handle was getting really personal. Try to think of something else. . . The curtain moved. Someone was standing on the other side of it. If her throat weren't so arid she might be able to scream. She could feel the presence through the cloth. Any moment now, someone was going to twitch the curtain aside. She leapt, or as close to a leap as was feasible-it was a kind of vertical lumber, billowing the curtain aside, colliding with a slim body behind it, and ending on the floor in a tangle of limbs and ripping velvet. She gulped air, and pressed down on the squirming bundle below her.

'I'll scream!' she said. 'And if I do your eardrums will come down your nose!' The writhing stopped. 'Perdifa?' said a muffled voice. Above her, the curtain-rail sagged at one end and the brass rings, one at a time, spun towards the floor. Nanny went back to the sacks. Each one bulged with round hard shapes that clinked gently under her questing finger. 'This is a lot of money, Walter,' she said carefully. 'Yes Mrs Ogg!' Nanny lost track of money fairly easily although this didn't mean the subject didn't interest her: it was just that, beyond a certain point, it became dream-like. All she could be sure of was that the amount in front of her would make anyone's drawers drop. 'I suppose,' she said, 'that if I was to ask you how it'd got here, you'd say it was the Ghost, yes? Like the roses?'

'Yes Mrs Ogg!' She gave him a worried look. 'You'll be all right down here, will you?' she said. 'You'll sit quiet? I reckon I need to talk to some people.'

'Where's my mum Mrs Ogg?'

'She's having a nice sleep, Walter.' Walter seemed satisfied with this. 'You'll sit quiet in your. . . in that room, will you?'

'Yes Mrs Ogg!'

'There's a good boy.' She glanced at the money-bags again. Money was trouble. Agnes sat back. André raised himself on his elbows and pulled the curtain off his face. 'What the hell were you doing there?' he said. 'I was- What do you mean, what was I doing there? You were creeping around!'

'You were hiding behind the curtain!' said André, getting to his feet and fumbling for the matches again. 'Next time you blow out a lamp, remember it'll still be warm.'

'We were. . . on important business. . .' The lamp glowed. André turned. 'We?' he said. Agnes nodded, and looked across at Granny. The witch hadn't moved, although it took a deliberate effort of will to focus on her among the shapes and shadows. André picked up the lamp and stepped forward. The shadows shifted. 'Well?' he said. Agnes strode across the room and waved a hand in the air. There was the chair back, there was the vase, there was. . . nothing else. 'But she was there!'

'A ghost, eh?' said André sarcastically. Agnes backed away. There is something about the light of a lamp held lower than someone's face. The shadows are wrong. They fall into unfortunate places. Teeth seem more prominent. Agnes came to realize that she was alone in a room in suspicious circumstances with a man whose face suddenly looked a lot more unpleasant than it had before. 'I suggest,' he said, 'that you get back to the stage right now, yes? That would be the very best thing you could do. And don't meddle in things that don't concern you. You've done too much as it is.'

The fear hadn't drained out of Agnes, but it had found a space in which to metamorphose into anger. 'I don't have to put up with that! For all I know, you might be the Ghost!'

'Really? I was told that Walter Plinge was the Ghost,' said André. 'How many people did you tell? And now it turns out that he's dead. . .'

'No, he's not!' It was out before she could stop it. She'd said it merely to wipe the sneer off his face. This happened. But the expression that replaced it was no improvement. A floorboard creaked. They both turned. There was a hat-stand in the corner, next to a bookcase. There were a few coats and scarves hanging from it. It was surely only the way that the shadows fell that made it look, from this angle, like an old woman. Or. . . 'Damn floors,' said Granny, fading into the foreground. She stepped away from the coats. As Agnes said, later: it wasn't as though she'd been invisible. She'd simply become part of the scenery until she put herself forward again; she was there, but not there. She didn't stand out at all. She was as unnoticeable as the very best of butlers. 'How did you get in?' said André. 'I looked all round the room!'

'Seein' is believin',' said Granny, calmly. 'Of course, the trouble is that believin' is also seein', and there's been too much of that round here lately. Now, I know you ain't the Ghost. . . so what are you, to be sneaking around in places where you shouldn't be?'

'I could ask you the same quest-'

'Me? I'm a witch, and I'm pretty good at it.'

'She's, er, from Lancre. Where I come from,' Agnes mumbled, trying to look at her feet. 'Oh? Not the one who wrote the book?' said André. 'I've heard people talking about-'

'No! I'm much worse than her, understand?'

'She is,' mumbled Agnes. André gave Granny a long look, like a man weighing up his chances. He must have decided that they were bobbing along the ceiling. 'I. . . hang around in dark places looking for trouble,' he said. 'Really? There's a nasty name for people like that, ' snapped Granny. 'Yes,' said André. 'It's “policeman”.' Nanny Ogg climbed out of the cellars, rubbing her chin thoughtfully. Musicians and singers were still milling around, uncertain about what was going to happen next. The Ghost had had the decency to be chased and killed during the interval. In theory that meant there was no reason why there shouldn't be a third act, as soon as Herr Trubelmacher had scoured the nearby pubs and dragged the orchestra back. The show must go on. Yes, she thought, it has to go on. It's like the build-up to a thunderstorm. . . no. . . it's more like making love. Yes. That was a far more Oggish metaphor. You put everything you've got into it, so sooner or later there's a point where it's got to go on, because you can't imagine stopping. The stage manager could dock a couple of dollars from their wages and they'd still go on, and everyone knew it. And they would still go on. She reached a ladder and climbed slowly into the flies. She hadn't been certain. She needed to be certain now.

The fly loft was empty. She walked carefully along the catwalk until she was over the auditorium. The buzz of the audience came through the ceiling beneath her, slightly muffled. Light shone up at the point where the thick cable for the chandelier disappeared into the hole. She stepped out over the creaking trapdoor and peered down. Terrific heat almost frizzled her hair. A few yards below her hundreds of candles were burning. 'Dreadful if that lot fell down,' she said quietly. 'I 'spect this place'd go up like a haystack. . .' She let her gaze travel up and up .the cable to the point, at just about waist-height, where it was halfcut through. You'd never see it, if you weren't expecting to find it. Then her gaze dropped again, and moved across the gloomy, dusty floor until it found something half-hidden in the dust: Behind her, a shadow among the shadows rose to its feet, balanced itself carefully, and started to run. 'I knows about policemen,' said Granny. 'They've got big helmets and big feet and you can see them a mile off. There's a couple lurching around backstage. Anyone can see they're policemen. You don't look like one.' She turned the badge over and over in her hands. 'I ain't happy with the idea of secret policemen,' she said. 'Why do you need secret policemen?'

'Because,' said André, 'sometimes you have secret criminals.' Granny almost smiled. 'That's a fact,' she said. She peered at the small engraving on the back of the badge. 'Says here “Cable Street Particulars”. . .'

'There aren't many of us,' said André. 'We've only just started. Commander Vimes said that, since we can't do anything about the Thieves' Guild and the Assassins' Guild, we'd better look for other crimes. Hidden crimes. That need Watchmen with. . . different skills. And I can play the piano quite well. . ., 'What kind of skills have that troll and that dwarf got?' said Granny. 'Seems to me the only thing they're really good at is standing around looking obvious and stupiHah! Yes. . .'

'Right. And they didn't even need much training,' said André. 'Commander Vimes says they're the most obvious policemen anyone could think of. Incidentally, Corporal Nobbs has got some papers to prove he's a human being.'

'Forged?'

'I don't think so.' Granny Weatherwax put her head on one side. 'If your house was on fire, what's the first thing you'd take out of it?'

'Oh, Granny-' Agnes began. 'Hmm. Who set fire to it?' said André. 'You're a policeman, right enough.' Granny handed him his badge. 'You come to arrest poor Walter?' she said. 'I know he didn't murder Dr Undershaft. I was watching him. He was trying to unblock the privies all afternoon-'