Assumptions are the things you don't know you're making, which is why it is so disorienting the first time you take the plug out of a wash basin in Australia and see the water spiralling down the hole the other way round. The very laws of physics are telling you how far you are from home.

In New Zealand even the telephone dials are numbered anticlockwise. This has nothing to do with the laws of physics - they just do it differently there. The shock is that it had never occurred to you that there was any other way of doing it. In fact you had never even thought about it at all, and suddenly here it is - different. The ground slips.

Dialling in New Zealand takes quite a bit of concentration because every digit is where you least expect to find it. Try and do it quickly and you will inevitably misdial because your automatic habit jumps in and takes over before you have a chance to stop it. The habit of telephone dials is so deep that it has become an assumption, and you don't even know you're making it.

China is in the northern hemisphere, so its wash basins drain clockwise, like ours. Their telephone dials are numbered like ours. Both those things are familiar. But every single other thing is different, and the assumptions that you don't know you're making will only get you into trouble and confusion.

I had a kind of inkling that this would be the case from what little I knew of other people's experiences in China. I sat in the plane on the long flight to Beijing trying to unravel my habits, to unthink as it were, and feeling slightly twitchy about it.

I started buying copious quantities of aftershave. Each time the duty-free trolley came round I bought a bottle. I had never done anything like it before in my life. My normal, instinctive reaction had always been just to shake my head and carry on reading my magazine. This time I thought it would be more Zen-like to say, `Yes, all right. What have you got?' I was not the only person I caught by surprise.

`Have you gone completely mad? Mark asked me as I slipped a sixth different bottle into my hand baggage.

`I'm trying to challenge and subvert my own fundamental assumptions as to what constitutes rationally constructed behaviour.'

`Does that mean yes??

'I mean that I'm just trying to loosen up a bit,' I said. `An aeroplane doesn't give you much scope for arbitrary and alternative types of behaviour, so I'm just making the most of the opportunities that are offered.'

'I see.'

Mark shifted uncomfortably in his seat and frowned deeply into his book.

`What are you going to do with all that stuff?' he asked a while later over an airline meal.

`Dunno,' I said. `It's a problem, isn't it??

'Tell me, are you feeling nervous about something?

Yes.'

`What?'

`China.'

In the middle of one of the biggest, longest, noisiest, dirtiest thoroughfares in the world lives the reincarnation of a drowned princess, or rather, two hundred reincarnations of a drowned princess.

Whether these are two hundred different reincarnations of the same drowned princess, or the individual reincarnations of two hundred different drowned princesses, is something that the legends are a little vague about, and there are no reliable statistics on the incidence of princess-drownings in the area available to help clear the matter up.

If they are all the same drowned princess then she must have led a life of exquisite sinfulness to have had the conditions of her current lives repeatedly inflicted on her. Her reincarnations are constantly being mangled in ships' propellers, snared in fishermen's nets full of hooks, blinded, poisoned and deafened.

The thoroughfare in question is the Yangtze river, and the reincarnated princess is the Baiji, the Yangtze river dolphin.

`How do you rate our chances of seeing a dolphin? I asked Mark.

`I haven't the faintest idea,' he said. `It's very hard to get information about anything out of China, and most of it's confusing. But the dolphins are to be found - or not - in a just a few parts of the Yangtze. The main one is a stretch of the river about two hundred kilometres long centred on a town called Tongling in Anhui province. That's where there are people working on saving the baiji, and that's the main place we're headed for. We get to Tongling by boat from Nanjing, where there's a man called Professor Zhou who's a major authority on the animal. We get to Nanjing by train from Shanghai. We get to Shanghai by plane from Beijing. We've got a couple of days in Beijing first to get acclimatised and see if any of the travel arrangements are actually going to work out. We've got thousands of miles to cover and travel is meant to be insanely difficult.'

`Do we have much leeway if things go wrong?' I asked. `Which days are Professor Zhou and the others expecting us??

'Expecting us? said Mark. `What do you mean? They've never heard of us. You can't actually contact anyone in China. We'll be lucky to find them and even luckier if they agree to talk to us. In fact I'm only half certain they exist. We're going into completely unknown territory.'

We both peered out of the window. Darkness was falling over the largest nation on earth.

`There's just one last bottle left, sir,' said the cabin steward to me at that moment. `Would you like it before we close up the duty-free? Then you'll have the complete range.'

It was quite late at night as a rickety minibus delivered us to our hotel on the outskirts of Beijing. At least, I think it was the outskirts. We had no point of reference by which to judge what kind of area it was. The streets were wide and tree-lined but eerily silent. Any motor vehicle made a single and particular growl instead of merging with a general traffic hum. The streetlights had no diffusing glass covers, so the light they shed was sharp, highlighting each leaf and branch and precisely delineating their shapes against the walls. Passing cyclists cast multiple interweaving shadows on the road around them. The sense of moving in a geometric web was added to by the clack of billiard balls as they cannoned across small tables set up under the occasional street lamp.

The hotel was set in a small network of narrow side streets, and its facade was wildly decorated with the carved red dragons and gilded pagoda shapes which are the familiar stereotypes of China. We hefted our bags full of camera equipment, recording gear, clothes and aftershave into the lobby past the long glass counter displays of carved chopsticks, ginseng and herbal aphrodisiacs, and waited to check in.

I noticed an odd thing. It was one of those tiny little disorienting details, like the telephone dials in New Zealand, that tell you you are in a very distant and foreign country. I knew that the Chinese traditionally hold their table tennis bats the way we hold cigarettes. What I did not know was that they also hold their cigarettes the way we hold table tennis bats.

Our rooms were small. I sat on the edge of my bed, which was made for someone of half my height, and laid out my bewildering collection of aftershave bottles in a neat line next to two large and ornately decorated red and gold thermos flasks that were already standing on the bedside table. I wondered how I was going to get rid of them. I decided to sleep on the problem. I hoped I would be able to. I read a note in the hotel's directory of guest services with foreboding. It said: 'No dancing, clamouring, quarrelling, fisticuffings or indulging in excessive drinking and creating disturbances in public places for the sake of keeping a peaceful and comfortable environment. Guests are not permitted to bring pets and poultry into the hotel.'