'I never know how to avoid Piccadilly when I'm going home.'

Albert inhaled on his cigarette. I had given him the perfect opening on his favourite topic: shortcuts in central London. 'Well – '

'Take your journey tonight,' I interrupted him. 'How did you tackle it? You knew there would be heavy traffic… when did you leave… seven?'

'Seven-fifteen. Well, they went for a drink in the White Elephant Club in Curzon Street first. They could have walked from there to the Connaught, I know, but it might have started to rain and there'd be no cabs in Curzon Street at that time. The table at the Connaught Hotel Grill Room was for eight o'clock. No place for a big car like mine in Curzon Street. They're double-parked there by seven on some evenings at this time of year. I got there via Birdcage Walk, past Buckingham Palace and Hyde Park Corner… a long way round, you say. But when you've spent as many years driving in London as I have you…'

I let Albert's voice drone on as I asked myself why my wife told me she was spending the evening with Tessa when really she was having dinner in a hotel with Bret Rensselaer. 'Is that the time?' I said, looking at my watch while Albert was in full flow. 'I must go. Nice talking to you, Albert. You're a mine of information.'

Albert smiled. I could still hear Così fan Tutte from the Bentley's stereo when I was driving up the exit ramp.

I watched her as she took off her rain-specked headscarf. She wore a silk square only when she wanted to protect a very special new hairdo. She shook her head and flicked at her hair with her fingertips. Her eyes sparkled and her skin was pale and perfect. She smiled; how beautiful she seemed, and how far away.

'Did you eat out?' she said. She noticed the dining table with the unused place setting that Mrs Dias had left for me.

'I had a cheese roll in a pub.'

'That's the worst thing you could choose,' she said. Tat and carbohydrates: that's not good for you. There was cold chicken and salad prepared.'

'So did Tessa find another house?'

Alerted perhaps by my tone of voice, or by the way I stood facing her, she looked into my face for a moment before taking off her raincoat. 'I couldn't get to Tessa's tonight. Something came up.' She shook the raincoat and the raindrops flashed in the light.

'Work, you mean?'

She looked at me steadily before nodding. We had a tacit agreement not to ask questions about work. 'Something Rensselaer wanted,' she said, and kept looking at me as if challenging me to pursue it.

'I saw your car in the car park when I left but Security said you'd already gone.'

She walked past me to hang her coat in the hall. When she'd done that, she looked in the hall mirror and combed her hair as she spoke. 'There was a lot of stuff in the diplomatic bag this afternoon. Some of it needed translation and Bret's secretary has only A-level German. I went over the road and worked there.'

Claiming to be in the Foreign Office as an explanation of absence was the oldest joke in the Department. No one could ever be found in that dark labyrinth. 'You had dinner with Rensselaer,' I said, unable to control my anger any longer.

She stopped combing her hair, opened her handbag and dropped the comb into it. Then she smiled and said, 'Well, you don't expect me to starve, darling. Do you?'

'Don't give me all that crap,' I said. 'You left the building with Rensselaer at seven-fifteen. You were in his Bentley when he drove out of the garage. Then I discovered he'd left the reception desk at the Connaught as his contact number for the night-duty officer.'

'You haven't lost your touch, darling,' she said with ice in every syllable. 'Once a field man, always a field man – isn't that what they say?'

'It's what people like Cruyer and Rensselaer say. It's what people say when they are trying to put down the people who do the real work.'

'Well, now it's paid off for you,' she said. 'Now all your old expertise has enabled you to discover that I had dinner at the Connaught with Bret Rensselaer.'

'So why do you have to lie to me?'

'What lies? I told you I had to do some work for Rensselaer. We had dinner – a good dinner, with wine – but we were talking shop.'

'About what?'

She pushed past me into the front room and through into the dining room that opened from it in what designers call 'open plan'. She picked up the clean plates and cutlery that had been left for me. 'You know better than to ask me that.' She went into the kitchen.

I followed her as she put the plates on a shelf in the dresser. 'Because it's so secret?'

'It's confidential,' she said. 'Don't you have work that is too confidential to talk to me about?'

'Not in the grillroom of the Connaught, I don't.'

'So you even know which room we were in. You've done your homework tonight, haven't you.'

'What was I supposed to do while you're having dinner with the boss? Am I supposed to eat cold chicken and watch TV?^'

'You were supposed to be having a beer with a friend, and then collecting the children from their visit to my parents' house.'

'Oh, my God! I forgot. 'I clean forgot about the children,' I admitted.

'I phoned mother. I guessed you'd forget. She gave them supper and brought them here in a minicab. It's all right.'

'Good old Mum-in-law,' I said.

'You don't have to be bloody sarcastic about my mother,' said Fiona. 'It's bad enough trying to have an argument about Bret.'

'Let's drop it,' I said.

'Do what you like,' said Fiona. 'I've had enough talk for one night.' She switched off the light in the dining room, then opened the door of the dishwasher, closed it again, and turned it on. The sprays of the dishwasher beat on its steel interior like a Wagnerian drumroll. The noise made conversation impossible.

When I came from the bathroom, I expected to see Fiona tucked into the pillow and feigning sleep; she did that sometimes after we'd had a row. But this time she was sitting up in bed, reading some large tome with the distinctive cheap binding of the Department's library. She wanted to remind me that she was a dedicated wage slave.

As I undressed, I tried a fresh, friendly tone of voice. 'What did Bret want?'

'I wish you wouldn't keep on about it.'

There's nothing between you, is there?'

She laughed. It was a derisory laugh. 'You suspect me… with Bret Rensselaer? He's nearly as old as my father.'

'He was probably older than the father of that cipher clerk – Jennie something – who left just before Christmas.'

Fiona raised her eyes from her book; this was the sort of thing that interested her. 'You don't think she…? With Bret, you mean?'

'Internal Security sent someone to find out why she'd left without giving proper notice. She said she'd been having an affair with Bret. He'd told her they were through.'

'Good grief,' said Fiona. 'Poor Bret. I suppose the D-G had to be told.'

'The D-G was pleased to hear the girl had proper security clearance, and that was that.'

'How broad-minded of the old man. I'd have thought he would have been furious. Still, Bret isn't married. His wife left him, didn't she?'

'The suggestion was that Bret had sinned before.'

'And always with someone with proper security clearance. Well, good for Bret. So that's why you thought…' She laughed again. It was a genuine laugh this time. She closed her book but kept a finger in the page. 'He's going through the regular routine about the danger of security lapses.'

'I told him about Giles Trent,' I said. 'I kept Tessa out of it.'

'Bret has decided to talk to everyone personally,' said Fiona.

'Surely Bret doesn't suspect you?'

Fiona smiled. 'No, darling. Bret didn't take me to the Connaught to interrogate me over the bones of the last of this season's woodcock. He spent the evening talking about you.'