'Catch him! And there could be a kipper in it for you!' Greebo snarled happily. This was more like it. Opera had begun to pall for him the moment he realized that no one was going to pour a bucket of cold water over the singers. He understood chasing things. Besides, he liked to play with his friends.

Agnes saw the movement out of the corner of her eye. A figure had jumped out of one of the Boxes and was climbing up to the balcony. Then another figure clambered after it, scrambling over the gilt cherubs. Singers faltered in mid-note. There was no mistaking the leading figure. It was the Ghost. The Librarian was aware that the orchestra had stopped playing. Somewhere on the other side of the backcloth the singers had stopped too. There was a buzz of excited conversation and one or two cries. The hairs all over his body began to prickle. Senses designed to protect his species in the depths of the rainforest had adjusted nicely to the conditions of a big city, which was merely drier and had more carnivores. He picked up the discarded bow-tie and, with great deliberation, tied it around his forehead so that he looked like a really formal Kamikaze warrior. Then he threw away the opera score and stared blankly into space for a moment. He knew instinctively that some situations required musical accompaniment. This organ lacked what he considered the most basic of facilities, such as the Thunder pedal, a 128-foot Earthquake pipe and a complete keyboard of animal noises, but he was certain there was something exciting that could be done in the bass register. He stretched out his arms and cracked his knuckles. This took some time. And then he began to play. * * * The Ghost danced along the edge of the balcony, scattering hats and opera-glasses. The audience watched in astonishment, and then began to clap. They couldn't quite see how it fitted into the plot of the opera- but this was an opera, after all. He reached the centre of the balcony, trotted a little way up the aisle, and then turned and ran down again at speed. He reached the edge, jumped, jumped again, soared out into the auditorium. . . . . .and landed on the chandelier, which jingled and began to sway gently. The audience stood up and applauded as he climbed through the jangling tiers towards the central cable. Then another shape clambered over the edge of the balcony and loped along in pursuit. This was a stockier figure than the first man, one-eyed, broad in the shoulders and tapering at the waist; he looked evil in an interesting kind of way, like a pirate who really understood the words 'Jolly Roger'. He didn't even take a run but, when he reached the closest part to the chandelier, simply launched himself into space. It was clear that he wasn't going to make it. And then it wasn't clear how he did. Those watching through opera-glasses swore later that the man thrust out an arm which merely seemed to graze the chandelier and yet was then somehow able to swivel his entire body in mid-air: A couple of people swore even harder that, just as the man reached out, his fingernails appeared to grow by several inches. The huge glass mountain swung ponderously on its rope and, as it reached the end of the swing, Greebo swung out further, like a trapeze artist. There was an appreciative 'oo' from the audience. He twisted again. The chandelier hesitated for a moment at the extremity of its arc, and then swept back again. As it jangled and creaked over the Stalls the hanging figure swung upwards, let go and did a backward somersault that dropped him in the

middle of the crystals. Candles and prisms were scattered over the seats below. And then, with the audience clapping and cheering, he scrambled up the rope after the fleeing Ghost. Henry Lawsy tried to move his arm, but a fallen crystal had stapled the sleeve of his coat to his armrest. It was a quandary. He was pretty sure this wasn't supposed to happen, but he wasn't certain. Around him he could hear people hissing questions. 'Was that part of the plot?'

'I'm sure it must have been.'

'Oh, yes. Yes. It certainly was,' said someone further down the row, authoritatively. 'Yes. Yes. The famous chase scene. Indeed. Oh, yes. They did it in Quirm, you know.'

'Oh. . .yes. Yes, of course. I'm sure I heard about it. . ., 'I thought it was bloody good,' said Mrs Lawsy. 'Mother!'

'About time something interesting happened. You should've told me. I'd've put my glasses on.' Nanny Ogg pounded up the back stairs towards the fly loft. 'Something's gone wrong!' she muttered under her breath as she took the stairs two at a time. 'She reckons she's only got to stare at 'em and they're toffee in her hands, and then who has to sort it out afterwards, eh? Go on, guess. . .' The ancient wooden door at the top of the stairs gave way to Nanny Ogg's boot with Nanny Ogg's momentum behind it, and cracked open on to a big, shadowy space. It was full of running figures. Legs flickered in the light of lanterns. People were shouting. A figure ran straight towards her. Nanny sprang into a crouch, both thumbs on the cork of the badly shaken champagne bottle she held cradled under one arm. 'This is a magnum,' she said, 'and I'm not afraid to drink it!' The figure stopped. 'Oh, it's you, Mrs Ogg. . .' Nanny's infallible memory for personal details threw up a card. 'Peter, isn't it?' she said, relaxing. 'The one with the bad feet?'

'That's right, Mrs Ogg.'

'The powder I give you is working, is it?'

'They're a lot better now, Mrs Ogg-'

'So what's been happening?'

'Mr Salzella caught the Ghost!'

'Really?' Now that Nanny's eyes had-managed to discern some order in the chaos, she could see a cluster of people in the middle of the floor, around the chandelier. Salzella was sitting on the planking. His collar was torn and a sleeve had been ripped off his jacket, but he had a triumphant look in his eyes. He waved something in the air. It was white. It looked like a piece of a skull. 'It was Plinge!' he said. 'I tell you, it was Walter Plinge! Why are you all standing around? Get after him!'

'Walter?' said one of the men, doubtfully. 'Yes, Walter!' Another man hurried up, waving his lantern. 'I saw the Ghost heading up to the roof! And there was some big one-eyed bastard going after him like a scalded cat!' That's wrong, thought Nanny. Something wrong here. 'To the roof!' shouted Salzella.

'Hadn't we better get the flaming torches first?'

'Flaming torches are not compulsory!'

'Pitchforks and scythes?'

'That's only for vampires!'

'How about just one torch?'

'Get up there now! Understand?' * * * The curtains closed. There was a smattering of applause which was barely audible above the chatter from the audience. The chorus turned to one another. 'Was that supposed to happen?' Dust rained down. Stage-hands were scampering across the gantries far above. Shouts echoed among the ropes and dusty backdrops. A stage-hand ran across the stage, holding a flaming torch. 'Here, what's going on?' said a tenor. 'They've got the Ghost! He's heading for the roof! It's Walter Plinge!'

'What, Walter?'

'Our Walter Plinge?'

'Yes!' The stage-hand ran on in a trail of sparks, leaving the yeast of rumour to ferment in the ready dough that was the chorus. 'Walter? Surely not!'

'Weeelll. . . he's a bit odd, isn't he. . . ?'

'But only this morning he said to me, “It's a nice day Mr Sidney!” Just like that. Normal as anything. Well. . . normal for Walter. . .'

'As a matter of fact, it's always worried me, the way his eyes move as though they don't talk to each other-'

'And he's always around the place!'

'Yes, but he's the odd job man-'

'No argument about that!'

'It's not Walter,' said Agnes. They looked at her. 'That's who he said they're chasing, dear.'

'I don't know who they're chasing, but Walter's not the Ghost. Fancy anyone thinking Walter's the Ghost!' said Agnes, hotly. 'He wouldn't hurt a fly! Anyway, I've seen-'

'He's always struck me as a bit slimy, though.'

'And they say he goes down into the cellars a lot. What for, I ask myself? Let's face it. Fair's fair. He's crazy.'

'He doesn't act crazy!' said Agnes. 'Well, he always looks as though he's about to, you must admit. I'm going to see what's happening. Anyone coming?' Agnes gave up. It was a horrible thing to learn, but there are times when evidence gets trampled and the hunt is on. A hatch flew open. The Ghost clambered out, looked down, and slammed the hatch shut. There was a yowl from below. Then he danced across the leads until he reached the gargoyle-encrusted parapet, black and silver in the moonlight. The wind caught at his cloak as he ran along the very edge of the roof and dropped down again near another door. And a gargoyle was suddenly no longer a gargoyle, but a figure that reached down suddenly and twitched off his mask. It was like cutting strings. 'Good evening, Walter,' said Granny, as he sagged to his knees. 'Hello Missus Weatherwax!'

'Mistress,' Granny corrected him. 'Now stand up.' There was a growl further along the roof, and then a thump. Bits of trapdoor rose for a moment against the moonlight. 'It's nice up here, ain't it?' said Granny. 'There's fresh air and stars. I thought: up or down? But there's only rats down below.' In another swift movement she grabbed Walter's chin and tilted it, just as Greebo pulled himself on to the roof with prolonged murder in his heart. 'How does your mind work, Walter Plinge? If your house was on fire, what's the first thing you'd try to take out? Greebo stalked along the rooftop, growling. He liked rooftops in general, and some of his fondest memories involved them, but a trapdoor had just been slammed on his head and he was looking for anything he could disembowel. Then he recognized the shape of Walter Plinge as someone who had given him food. And, standing right next to him, the much more unwelcome shape of Granny Weatherwax, who had once caught him digging in her garden and had kicked him in the cucumbers. Walter said something. Greebo didn't take much notice of it. Granny Weatherwax said: 'Well done. A good answer. Greebo!' Greebo nudged Walter heavily in the back. 'Want milluk right noaow! Purr, purr!' Granny thrust the mask at the cat. In the distance people were running up stairs and shouting. 'You put this on! And you stay down real low, Walter Plinge. One man in a mask is pretty much like another, after all. And when they chase you, Greebo. . . give them a run for their money. Do it right and there could be-'

'Yurr, I knoaow,' said Greebo despondently, taking the mask. It was turning out to be a long and busy evening for a kipper. Someone poked their head out of the stricken trapdoor. The light glinted off Greebo's mask. . . and it had to be said, even by Granny, that he made a good Ghost. For one thing, his morphogenic field was trying to reassert itself. His claws could no longer even remotely be thought of as fingernails. He spat at the pursuit as they poured up the steps, arched his back dramatically on the very edge of the roof, and stepped off. One storey down he thrust out an arm, caught a windowsill, and landed on the head of a gargoyle, which said 'Oh, fank oo ver' mush' in a reproachful voice. The pursuers looked down at him. Some of them had managed to get hold of flaming torches, because sometimes convention is too strong to be lightly denied. Greebo snarled defiance and dropped again, springing from sill to drainpipe to balcony and pausing every now and again for another dramatic pose and another snarl at the pursuers. 'We'd better get after him, Corporal de Nobbs,' said one of them, who was staggering along behind. 'We'd better get after him by carefully going back down the stairs, you mean. 'Cos somethin' I drank don't want to stay drunk. Much more runnin' and I'll be droppin' a custard, I'm tellin' you.' The other members of the posse also seemed to be reaching the conclusion that there was no extended future in chasing a man down the sheer wall of a building. As one mob they turned and, shouting and waving their torches in the air, headed back to the stairs. The parting crowd revealed Nanny Ogg, holding a pitchfork in one hand and a torch in the other and thrusting them both in the air while muttering, 'Rhubarb, rhubarb.'