I gawped, looking to a passing bee for reassurance. Surely Mark couldn't be slaveringly respectful of this?

"Ye-es," he said doubtfully. "Well I'm not sure ..."

"Giles seems to be very keen on Bridget!" Rebecca burst in, obviously sensing she had veered off course.

There was a pause. Then Mark said, in an unusually high-pitched voice, "Oh really. And is ... is this reciprocated?"

"Oh, you know Bridget," said Rebecca airily. "I mean Jude says she's got all these guys after her" - Good old Jude, I started to think - "but she's so screwed up she won't - well, as you say, she can't get it together with any of them."

"Really?" Mark jumped in. "So have there been ..."

"Oh, I think - you know - but she's so bogged down in her rules of dating or whatever it is that no one's good enough."

Could not work out what was going on. Maybe Rebecca was trying to make him stop feeling guilty about me.

"Really?" said Mark again. "So she isn't ..."

"Oh, look, there's a duckling! Oh, look, a whole brood of ducklings! And there's the mother and father. Oh, what a perfect, perfect moment! Oh, let's go look!"

And off they went, and I was left, breathless, mind racing.

After lunch, it was boiling hot and everyone decamped under a tree at the edge of the lake. It was an idyllic, pastoral scene: an ancient stone bridge over the water, willows overhanging the grassy banks. Rebecca was triumphant. "Oh, this is such fund! Isn't it, everyone? Isn't it fun?"

Fat Nigel from Mark's office was fooling about heading a football to one of the hoorays, huge stomach quivering in the bright sunlight. He made a lunge, missed and plunged head-first into the water, displacing a giant wave.

"Yesss!" said Mark, laughing. "Breathtaking incompetence."

"It's lovely, isn't it?" I said vaguely to Shaz. "You expect to see lions lying down with lambs."

"Lions, Bridget?" said Mark. I started. He was sitting right at the other side of the group, looking at me through a gap in the other people, raising one eyebrow.

"I mean like in psalm whatsit," I explained.

"Right," he said. There was a familiar teasing look in his eye. "Do you think you might be thinking of the Lions of Longleat?"

Rebecca suddenly leaped to her feet. "I'm going to jump off the bridge!"

She looked round beaming expectantly. Everyone else was in shorts or little dresses, but she was naked except for a tiny sliver of Calvin Klein brown nylon.

"Why?" said Mark.

"Because attention was diverted from her for five minutes," breathed Sharon.

"We used to do it when we were little! It's heaven!"

"But the water's very low," said Mark.

It was true, there was a foot and a half of baked earth all the way round the water line.

"No, no. I'm good at this, I'm very brave."

"I really don't think you should, Rebecca," said Jude.

"I have made up my mind. I am resolute!" she twinkled archly, slipped on a pair of Prada mules, and sashayed off towards the bridge. Happily, there was a bit of mud and grass attached to her upper right-hand buttock, which greatly added to the effect. As we watched, she took off the mules, held them in her hand and climbed on to the edge of the parapet.

Mark had got to his feet, looking worriedly at the water and up at the bridge.

"Rebecca!" he said. "I really don't think ..."

"It's all right, I trust my own judgement," she said playfully, tossing her hair. Then she looked upwards, raised her arms, paused dramatically and jumped.

Everyone stared as she hit the water. The moment came when she should have reappeared. She didn't. Mark started towards the lake just as she broke the surface screaming.

He ploughed off towards her as did the other two boys. I reached in my bag for my mobile.

They pulled her to the shallows and eventually, after much writhing and crying, Rebecca came limping to shore, supported between Mark and Nigel. it was clear that nothing too terrible could have happened.

I got up and handed her my towel. "Shall I dial 999?" I said as a sort of joke.

"Yes ... yes."

Everyone gathered round staring at the injured hostess's foot. She could move her toes, daintily and professionally painted in Rouge Noir, so that was a blessing.

In the end I got the number of her doctor, took the out-of-surgery hours number from the answerphone, dialled it and handed the phone to Rebecca.

She spoke at length to the doctor, moving her foot according to his instructions and making a great range of noises, but in the end it was agreed there was no breakage, not really a sprain, just a slight jar.

"Where's Benwick?" said Nigel, as he dried himself and helped himself to a big slug of chilled white wine.

"Yes, where is Giles?" said Louise Barton-Foster. "I haven't seen him all morning."

"I'll go and see," I said, grateful to get away from the hellish sight of Mark rubbing Rebecca's delicate ankle.

It was nice to get into the cool of the entrance hall with its sweeping staircase. There was a line of statues on marble plinths, oriental rugs on the flagstone floor, and another of the giant garish crests above the door. I stood for a moment, relishing the peace. "Giles?" I said and my voice echoed round and round. "Giles?"

There was no reply. I had no idea where his room was, so set off up the magnificent staircase.

"Giles!" I peeked into one of the rooms and saw a gigantic carved-oak four-poster bed. The whole room was red and it looked out over the scene with the lake. The red dress Rebecca had been wearing at dinner was hanging over the mirror. I looked at the bed and felt as though I had been punched in the stomach. The Newcastle United boxer shorts I bought Mark for Valentine's Day were neatly folded on the bedspread.

I shot out of the room and stood with my back to the door, breathing unsteadily. Then I heard a moan.

"Giles?" I said. Nothing. "Giles? It's Bridget."

The moaning noise came again.

I walked along the corridor. "Where are you?"

"Here."

I pushed open the door. This room was lurid green and hideous with huge lumps of dark wood furniture everywhere. Giles was lying on his back with his head turned to one side, moaning slightly, the telephone off the hook beside him.

I sat on the bed and he opened his eyes slightly and closed them again. His glasses were skew-whiff on his face. I took them off

"Bridget." He was holding a bottle of pills. I took them from him. Temazepam.

"How many have you taken?" I said, taking his hand.

"Six ... or four?'

"When?"

"Not long ... about ... not long."

"Make yourself sick," I said, thinking that they always pumped overdosed people's stomachs.

We went together into the bathroom. It wasn't attractive, frankly, but then I gave him lots of water and he flopped back on the bed and started to sob quietly, holding my hand. He had called Veronica, his wife, it emerged groaningly, as I stroked his head. And he had lost all sense of himself and self-respect by begging her to come back, thereby undoing all his good dignified work of the last two months. At this, she'd announced she definitely wanted a divorce and he felt desperate, which I could totally relate to. As I told him, it was enough to drive anyone to the Temazepam.

There were footsteps in the corridor, a knock, and then Mark appeared in the doorway.

"Will you ring the doctor again?" I said.

"What's he taken?"

"Temazepam. About half a dozen. He's been sick."

He stepped out in the corridor. There were more voices. I heard Rebecca go "Oh, for God's sake!" and Mark trying to quieten her down, then more low mumbling.

"I just want everything to stop. I don't want to feel like this. I want it all just to stop," moaned Giles.

"No, no," I said. "You have to have hope and confidence that everything will turn out all right, and it will."