' Yes!'

There was then a pause.

'No obviously not,' said the bird after a few seconds. 'Good, well your hearing range is obviously between 20 and 16 KHz. So. Is this comfortable for you?' it said in a pleasant light tenor. 'No uncomfortable harmonics screeching away in the upper register? Obviously not. Good. I can use those as data channels. Now. How many of me can you see?'

Suddenly the air was full of nothing but interlocking birds.

Random was well used to spending time in virtual realities, but this was something far weirder than anything she had previously encountered. It was as if the whole geometry of space was redefined in seamless bird shapes.

Random gasped and flung her arms round her face, her arms moving through bird-shaped space.

'Hmmm, obviously way too many,' said the bird. 'How about now?'

It concertina-ed into a tunnel of birds, as if it was a bird caught between parallel mirrors, reflecting infinitely into the distance.

'What are you?' shouted Random.

'We'll come to that in a minute,' said the bird. 'Just how many, please?'

'Well, you're sort of …' Random gestured helplessly off into the distance.

'I see, still infinite in extent, but at least we're homing in on the right dimensional matrix. Good. No, the answer is an orange and two lemons.'

'Lemons?'

'If I have three lemons and three oranges and I lose two oranges and a lemon what do I have left?'

'Huh?'

'OK, so you think that time flows that way, do you? Interesting. Am I still infinite?' it asked, ballooning this way and that in space. 'Am I infinite now? How yellow am I?'

Moment by moment the bird was going through mind-mangling transformations of shape and extent.

'I can't . . .' said Random, bewildered.

'You don't have to answer, I can tell from watching you now. So. Am I your mother? Am I a rock? Do I seem huge, squishy and sinuously intertwined? No? How about now? Am I going backwards?'

For once the bird was perfectly still and steady.

'No,' said Random.

'Well I was in fact, I was moving backwards in time. Hmmm. Well I think we've sorted all that out now. If you'd like to know, I can tell you that in your universe you move freely in three dimensions that you call space. You move in a straight line in a fourth, which you call time, and stay rooted to one place in a fifth, which is the first fundamental of probability. After that it gets a bit complicated, and there's all sorts of stuff going on in dimensions 13 to 22 that you really wouldn't want to know about. All you really need to know for the moment is that the universe is a lot more complicated than you might think, even if you start from a position of thinking it's pretty damn complicated in the first place. I can easily not say words like «damn» if it offends you.'

'Say what you damn well like.'

'I will.'

'What the hell are you?' demanded Random.

'I am The Guide. In your universe I am your Guide. In fact I inhabit what is technically known as the Whole Sort of General Mish Mash which means . . . well, let me show you.'

It turned in mid-air and swooped out of the cave, and then perched on a rock, just beneath an overhang, out of the rain, which was getting heavier again.

'Come on,' it said, 'watch this.'

Random didn't like being bossed around by a bird, but she followed it to the mouth of the cave anyway, still fingering the rock in her pocket.

'Rain,' said the bird. 'You see? Just rain.'

'I know what rain is.'

Sheets of the stuff were sweeping through the night, moonlight sifting through it.

'So what is it?'

'What do you mean, what is it? Look, who are you? What were you doing in that box? Why have I spent a night running through the forest fending off demented squirrels to find that all I've got at the end of it is a bird asking me what rain is. It's just water falling through the bloody air, that's what it is. Anything else you want to know or can we go home now?'

There was a long pause before the bird answered, 'You want to go home?'

'I haven't got a home!' Random almost shocked herself, she screamed the words so loudly.

'Look into the rain . . .' said the bird Guide.

'I'm looking into the rain! What else is there to look at?'

What do you see?'

'What do you mean, you stupid bird? I just see a load of rain. It's just water, falling.'

'What shapes do you see in the water?'

'Shapes? There aren't any shapes. It's just, just . . .

'Just a mish mash,' said the bird Guide.

'Yes . . .'

'Now what do you see?'

Just on the very edge of visibility a thin faint beam fanned out of the bird's eyes. In the dry air beneath the overhang there was nothing to see. Where the beam hit the drops of rain as they fell through it, there was a flat sheet of light, so bright and vivid it seemed solid.

'Oh great. A laser show,' said Random fractiously. 'Never seen one of those before, of course, except at about five million rock concerts.'

'Tell me what you see!'

'Just a flat sheet! Stupid bird.'

'There's nothing there that wasn't there before. I'm just using light to draw your attention to certain drops at certain moments. Now what do you see?'

The light shut off.

'Nothing.'

'I'm doing exactly the same thing, but with ultra-violet light. You can't see it.'

'So what's the point of showing me something I can't see?'

'So that you understand that just because you see something, it doesn't mean to say it's there. And if you don't see something it doesn't mean to say it's not there, it's only what your senses bring to your attention.'

'I'm bored with this,' said Random, and then gasped.

Hanging in the rain was a giant and very vivid three-dimen– sional image of her father looking startled about something.

About two miles away behind Random, her father, struggling his way through the woods suddenly stopped. He was startled to see an image of himself looking startled about something hanging brightly in the rain-filled air about two miles away. About two miles away some distance to the right of the direction in which he was heading.

He was almost completely lost, convinced he was going to die of cold and wet and exhaustion and beginning to wish he could just get on with it. He had just been brought an entire golfing magazine by a squirrel, as well, and his brain was beginning to howl and gibber.

Seeing a huge bright image of himself light up in the sky told him that, on balance, he was probably right to howl and gibber but probably wrong as far as the direction he was heading was concerned.

Taking a deep breath, he turned and headed off towards the inexplicable light show.

'OK, so what's that supposed to prove?' demanded Random. It was the fact that the image was her father that had startled her rather than the appearance of the image itself. She had seen her first hologram when she was two months old and had been put in it to play. She had seen her most recent one about half an hour ago playing the March of the AnjaQantine Star Guard.

'Only that it's no more there or not there than the sheet was,' said the bird. 'It's just the interaction of water from the sky moving in one direction, with light at frequencies your senses can detect moving in another. It makes an apparently solid image in your mind. But it's all just images in the Mish Mash. Here's another one for you.'

'My mother!' said Random.

'No,' said the bird.

'I know my mother when I see her!'

The image was of a woman emerging from a spacecraft inside a large, grey hangar-like building. She was being escorted by a group of tall, thin purplish-green creatures. It was definite– ly Random's mother. Well, almost definitely. Trillian wouldn't have been walking quite so uncertainly in low gravity, or looking around her at a boring old life-support environment with quite such a disbelieving look on her face, or carrying such a quaint old camera.