In alarm I quickly looked round for Dad but couldn't see him anywhere. I saw Mark Darcy talking to Una and gesturing in my direction then Una, looking purposeful, hurried across to me.

'Bridget, I am so sorry about the mix-up over the fancy dress,' she said. 'Mark was just saying you must feel dreadfully uncomfortable with all these older chaps around. Would you like to borrow something?'

I spent the rest of the party wearing, over my suspender outfit, a puff-sleeved, floral-sprig Laura Ashley bridesmaid dress of Janine's with Mark Darcy's Natasha smirking and my mother periodically rushing past going, 'That's a pretty dress, darling. Cut!'

'I don't think much of the girlfriend, do you? said Una Alconbury loudly, nodding in Natasha's direction as soon as she got me alone. 'Very much the Little Madam. Elaine thinks she's desperate to get her feet under the table. Oh, hello, Mark! Another glass of Pimms? What a shame Bridget couldn't bring her boyfriend. He's a lucky chap, isn't he?' All this was said very aggressively as if Una was taking as a personal insult the fact that Mark had chosen a girlfriend who was a) not me and b) had not been introduced to him by Una at a turkey curry buffet. 'What's his name, Bridget? Daniel, is it? Pam says he's one of these sooper-dooper young publishers.

'Daniel Cleaver?' said Mark Darcy.

'Yes, it is, actually,' I said, jutting my chin out.

'Is he a friend of yours, Mark?' said Una.

'Absolutely not,' he said, abruptly.

'Oooh. I hope he's good enough for our little Bridget,' Una pressed on, winking at me as if this was all hilarious fun instead of hideous.

'I think I could say again, with total confidence, absolutely not,' said Mark.

'Oh, hang on a tick, there's Audrey. Audreyl' said Una, not listening, and tripping off, thank God.

'I suppose you think that's clever,' I said furiously, when she'd gone.

'What?' said Mark, looking surprised.

'Don't you "What?" me, Mark Darcy,' I muttered.

'You sound just like my mother,' he said.

'I suppose you think its all right to slag people's boyfriends off to their parents' friends behind their back when they're not even there for no reason just because you're jealous,' I flailed.

He stared at me, as if distracted by something else. 'Sorry,' he said. 'I was just trying to figure out what you mean. Have I . . .? Are you suggesting that I am jealous of Daniel Cleaver? Over you?'

'No, not over me,' I said, furious because I realized it did sound like that. 'I was just assuming you must have some reason to be so horrible about my boyfriend other than pure malevolence.'

'Mark, darling,' cooed Natasha, tripping prettily across the lawn to join us. She was so tall and thin she hadn't felt the need to put heels on, so could walk easily across the lawn without sinking, as if designed for it, like a camel in the desert. 'Come and tell your mother about the dining furniture we saw in Conran.'

'Just take care of yourself, that's all, he said quietly, 'and I'd tell your mum to watch out for herself too,' he said, nodding pointedly in the direction of Julio as Natasha dragged him off.

After 45 minutes more horror I thought I could decently leave, pleading work to Una.

'You career girls! Can't put it off forever you know: tick-tock-tick-tock,' she said.

I had to have a cigarette in the car for five minutes before I was calm enough to set off. Then just as I got back to the main road my dad's car drove past. Sitting next to him in the front seat was Penny Husbands-Bosworth, wearing a red lace underwired uplift basque, and two bunny ears.

By the time I got back to London and off the motorway I was feeling pretty shaky and back much earlier than I expected, so I thought, instead of going straight home, I'd go round to Daniel's for a bit of reassurance.

I parked nose to nose with Daniel's car. There was I no answer when I rang, so I left it a while and rang again in case it was just in the middle of a really good wicket or something. Still no answer. I knew he must be around because his car was there and he'd said he was going to be working and watching the cricket. I looked up at his window and there was Daniel. I beamed at him, waved and pointed at the door. He disappeared, I assumed to press the buzzer, so I rang the bell again. He took a bit of time to answer: 'Hi, Bridge Just the on phone to America. Can I meet you in the pub in ten minutes?'

'OK,' I said cheerfully, without thinking, and set off towards the comer. But when I looked round, there he was again, not on the phone, but watching me out of the window.

Cunning as a fox, I pretended not to see and kept walking, but inside I was in turmoil. Why was he watching? Why hadn't he answered the door first time? Why didn't he just press the buzzer and let me come up straight away? Suddenly it hit me like a thunderbolt. He was with a woman.

My heart pounding, I rounded the corner, then, keeping flat against the wall, I peered round to check he had gone from the window. No sign of him. I hurried back and assumed a crouching position in the porch next to his, observing his doorway between the pillars in case a woman came out. I waited, crouched in the position for some time. But then I started to think: if a woman did come out, how would I know it was Daniel's flat she had come out of and not one of the other flats in the building? What would I do? Challenge her? Make a citizen's arrest? Also, what was to stop him leaving the woman in the flat with instructions to stay there until he had had time to get to the pub?

I looked at my watch. 6.30. Hah! The pub wasn't open yet. Perfect excuse. Emboldened, I hurried back towards the door and pushed the buzzer.

'Bridget, is that you again?' he snapped.

'The pub isn't open yet.'

There was silence. Did I hear a voice in the background? In denial, I told myself he was just laundering money or dealing in drugs. He was probably trying to hide polythene bags full of cocaine under the floorboards helped by some smooth South American men with ponytails.

'Let me in,' I said.

' I told you, I'm on the phone.'

'Let me in.'

'What?' He was playing for time I could tell.

'Press the buzzer, Daniel,' I said.

Isn't it funny how you can detect someone's presence, even though you can't see, hear or otherwise discern them? Oh of course I'd checked the cupboards on the way up the stairs and there was no one in any of them. But I knew there was a woman in Daniel's house. Maybe it was a slight smell . . . something about the way Daniel was behaving. Whatever it was, I just knew .

We stood there warily at opposite sides of the sitting room. I was just desperate to start running around opening and dosing all the cupboards like my mother and ringing 1471 to see if there was a number stored from America.

'What have you got on?' he said. I had forgotten about Janine's outfit in the excitement.

'A bridesmaid's dress,' I said, haughtily.

'Would you like a drink?' said Daniel. I thought fast. I needed to get him into the kitchen so I could go through all the cupboards.

'A cup of tea, please.'

'Are you all right?' he said.

'Yes! Fine!' I trilled. 'Marvellous time at the party. Only one dressed as a tart, had to put on a bridesmaid dress, Mark Darcy was there with Natasha, that's a nice shirt your wearing . . .' I stopped, out of breath, realizing I had turned (there was no 'was turning' about it) into my mother.

He looked at me for a moment, then set off into the kitchen at which I quickly leapt across the room to look behind the sofa and the curtains.

'What are you doing?'

Daniel was standing in the doorway-

'Nothing, nothing. Just thought I might have left a skirt of mine behind the sofa,' I said, wildly plumping up the cushions as if I were in a French farce.

He looked suspicious and headed off to the kitchen again.

Deciding there was no time to dial 1471, I quickly checked the cupboard where he keeps the duvet for the sofabed – no human habitation – then followed him to the kitchen, pulling open the door of the hall cupboard as I passed at which the ironing board fell out, followed by a cardboard box full of old 45s which slithered out all over the floor.

'What are you doing?' said Daniel mildly again, coming out of the kitchen.

'Sorry, just caught the door with my sleeve, I said. just on my way to the loo.'

Daniel was staring at me as if I was mad, so I couldn't go and check the bedroom. Instead I locked the loo door and started frantically looking around for things. I wasn't exactly sure what, but long blonde hairs, tissues with lipstick marks on, alien hairbrushes – any of these would have been a sign. Nothing. Next I quietly unlocked the door, looked both ways, slipped along the corridor, pushed open the door of Daniel's bedroom and nearly jumped out of my skin. There was someone in the room.

'Bridge.' It was Daniel, defensively holding a pair of jeans in front of him. 'What are you doing in here?'

'I heard you come in here so . . . I thought . . . It was secret assignation,' I said, approaching him in what would have been a sexy way were it not for the floral sprig dress. I leaned my head on his chest and put my arms around him, trying to smell his shirt for perfume traces and get a good look at the bed, which was unmade as usual.

'Mmmm, you've still got the bunny girl outfit on underneath, haven't you?' he said, starting to unzip the bridesmaid dress and pressing against me in a way which made his intentions very clear. I suddenly thought this might be a trick and he was going to seduce me while the woman slipped out unnoticed.

'Oooh, the kettle must be boiling, said Daniel suddenly, zipping my dress up again and patting me reassuringly in a way that was most unlike him. Usually once he gets going he will see things through to their logical conclusion come earthquake, tidal wave or naked pictures of Virginia Bottomley on the television.

'Ooh yes, better make that cuppa,' I said, thinking it would give me a chance to get a good look round the bedroom and scout the study.

'After you,' said Daniel, pushing me out and shutting the door so I had to walk ahead of him back into the kitchen. As I did so I suddenly caught sight of the door that led up to the roof terrace.

'Shall we go and sit down?' said Daniel.

T'hat was where she was, she was on the bloody roof.

'What's the matter with you?' he said as I stared at the door suspiciously.

'No-thing,' I sing-songed gaily, flopping into the sitting room. 'Just a little tired from the party.'

I flung myself insouciantly on to the sofa, wondering whether to streak faster than the speed of light down to the study as the final place she might be or just go hell for leather for the roof I figured if she wasn't on the roof it meant she must be in the study' in the bedroom wardrobe, or under the bed. If we then went up on the roof she would be able to escape. But if that was the case, surely Daniel would have suggested going up on the roof much sooner.