Shafiq was going from baffled to slightly annoyed. 'What are we looking for, Michael? Perhaps I could suggest something else. The CCTV looks at all the doors and even the ventilation shafts.'

'I'm sorry to trouble you, Shafiq, but please show me.'

The cold room looked grey and indistinct and empty. It was hard to see; for a moment Michael thought he saw something move, as if through fog. He peered, but was finally sure beyond doubt. There was no one there.

The security video jumped between frames taken one second apart. Suddenly, the door was half-open. Suddenly it was wide open. Suddenly Michael himself stepped in in stages, lurching like Frankenstein's monster. He stayed alone and chatting to no one.

'OK, Shafiq. False alarm.'

Shafiq stood up straight and adjusted his blue shirt. 'But if there has been anything moved, surely it would be better to study tapes when you weren't there.'

Michael closed his eyes, to avoid Shafiq's face, and his voice was unnaturally quiet and precise. 'I was mistaken, Shafiq. I don't want to worry you further. Thank you for helping.'

He walked out of the room, his back held straight.

In the corridor he thought, I'm alone. I'm really alone.

Maybe I am just crazy.

But even if I'm not, they aren't real. My Angel said that. They are the universe breaking its own rules. If unreal people walked free to change the world, it would be a catastrophe. And so they come and work and love and when they leave, they leave no evidence or trace behind.

They can't sort slides; they can't be video taped.

The only evidence, the only scars, will be in my memory. I am the only thing they can change. Otherwise, poor Angels, when they go it is as if they never existed.

Michael felt sad for them. Because I know that when they are here, they love and feel and want. When they're here, they're alive.

Michael sat at his desk and looked at the brick wall again, and heard his own voice rage, demanding, 'Why is the design of this experiment such crap!'

What is a sample of one going to tell you, God? Why bend all the rules of the universe just to do this terrible thing to me? Is it a joke, God? Does it amuse you to see people knocked sideways, their whole life go rotten like an apple? Do you like to see us hauled beyond our limits? Do you like to see us cry?

And why do this to an impotent man? What is it going to teach me, what are you going to learn from this except what we both know? I'm lousy in bed. What's the big deal about that, I live with it, I've learned to live with it.

Michael went back to the cold room. In a rage, sweating in the chill, he tore through the work. The glass edges of the slides cut his fingers.

It took an hour. When he was done he had a sudden moment of irrational fear that his own work would also disappear. He closed the drawer and opened it again, to check. The work remained.

So maybe I do just make them up, maybe I make up that other people see and hear them. Maybe I am just nuts.

Michael arrived back at the flat late, exhausted, chilled and sweaty. He must have looked a state. Phil glanced up at him from what looked like a plate of tomato sauce on cardboard. 'You didn't tell me when you would be home,' Phil said. 'So I went ahead with dinner.'

So when did Phil ever call to say when he'd be home? Michael sat down exhausted, shambolic. Today was a bad hair day: his scalp itched and he knew his hair tumbled down in dank, greasy curls. His five o'clock shadow had arrived on time, but now, at 8.30 pm, it was even thicker and coated with cold sweat. Phil wouldn't look at him.

'That's OK, I guess,' said Michael. 'You probably don't realize that I've been coming home on time lately. You're never in. It was my effort to be here in case you wanted to go to a movie or anything.'

Phil's eyes were shuttered like windows. In the silence, Michael had the opportunity to examine Phil's newly vegetarian food. There was no table fat on his bread.

Phil asked in a light voice, 'Where exactly is your work?'

It was a question that produced an automatic prickling sensation of suspicion, even fear. Hold on, thought Michael. This is Phil. Then he thought, hold on, this is Phil.

He stalled. 'What do you mean?'

'Oh. It's just that you've never told me, that's all. It can't be that long a trip. Waterloo, isn't it?'

' Waterloo? No! No, no, the Elephant and Castle.'

Phil shrugged elaborately and his eyes didn't move from the plate. 'I thought it was Waterloo.' His tiny mouth had to stretch to take a bite out of a chunk of bread that was the colour of brown shoes. 'In an old warehouse or something.'

Michael began to trace the criss-cross patterns of green on the waterproof tablecloth. I've never said in an old warehouse or anything else. Certainly not in the arches underneath an elevated railway.

'Yeah, an old warehouse. Near the Old Kent Road.'

Phil nodded now, very carefully, very slowly.

Michael pressed together his thick veined hands.

My boyfriend is pumping me for my work address so he can give it to animal rights demonstrators. My boyfriend of thirteen years wants to betray me. Henry has such a nice smile, doesn't he?

'So how is the gorgeous Henry?' The emphasis on the 'is' somehow made it plain that Michael had been reminded of Henry by the previous topic, that there was a connection between them.

'He's fine, thank you,' said Phil, coolly.

He doesn't even care that I've guessed.

Michael struck back. It was a bit like playing tennis. 'You know many couples in our situation would be busy reassuring each other that they practised safe sex with their lovers. They'd talk about whether they should be using condoms with each other. But

Michael considered letting his voice trail delicately away, but you play tennis to win. 'But we don't have to, do we Phil? We don't make love.'

It was only then, finally, that Michael realized he needed a new life.

Can they give me Aids?

After California, Michael spent the next ten years missing sexual opportunities. As these years were 1976 to 1986, missing opportunities probably saved his life.

Everyone else was going at it like ferrets, not knowing there was something brand-new in the world. By the time Michael emerged from purdah, he and the world knew things had changed, and were taking precautions.

But it was already too late for several dear friends. They rolled on all unknowing for many years, all through the eighties into the nineties, though they were, like Shrodinger's cat, already dead mathematically. They had the virus. Or rather, it had them.

If you can have sex with anyone in the world, you need to know as a matter of urgency, if they can make you ill. Answering this question presented Michael with several interesting methodological difficulties.

If he experimented on himself and it made him ill, that would indeed be a result, but it would rather defeat the purpose. On the other hand, experimenting on someone else did raise certain ethical questions.

It was also methodologically suspect. Michael would first have to ensure that whoever was being tested was HIV negative to begin with. Proving HIV negative status is extremely difficult. Antibodies take three months to show up after infection. That means a second test is necessary three months after the first. During those three months, you have to know absolutely that the person has avoided all risk of exposure to the virus. That means no kissing. If there are any doubts, you have to test again three months after that.

If the subject was, say, a nun who never had sex with anyone, Michael would first have to find the one Angel in the world who could seduce her, and then persuade her that she needed an HIV test. This scenario seemed unlikely.