‘LH?’ I said, tentatively.

‘Light helicopter,’ Sarah answered, with an ‘imagine not knowing that’ expression. Woolf senior pressed on.

‘This aircraft is a response to that programme. It’s a product of the Mackie Corporation ofAmerica, and is designed for use in counter-insurgency operations. Terrorism. The market for it, outside of the Pentagon’s procurement, is among police and militia forces around the world. But at two-and-a-half million dollars each, they’re going to be hard to shift.’

‘Yes,’ I said. ‘I can see that.’ I glanced at the pictures again and scrabbled for something intelligent to say. ‘Why the two rotors? Looks a bit complicated.’ I caught them looking at each other, but couldn’t tell you what the look meant.

‘You don’t know anything about helicopters, do you?’ said Woolf, eventually.

I shrugged.

‘They’re noisy,’ I said. ‘They crash a lot. That’s about it.’

‘They’re slow,’ said Sarah. ‘Slow, and therefore vulnerable on a battlefield. The modern attack helicopter can travel at around two-hundred-and-fifty miles an hour.’

I was about to say that that sounded pretty slippy to me, when she continued: ‘A modern fighter airplane will cover a mile in four seconds.’

Without summoning a waiter and asking for a pencil and paper, there was not the remotest chance of my working out whether this was faster or slower than two hundred and fifty miles an hour, so I just nodded and let her carry on.

‘What limits the speed of a conventional helicopter,’ she said slowly, sensing my discomfort, ‘is the single rotor.’

‘Naturally,’ I said, and settled back in my seat for Sarah’s impressively expert lecture. A lot of what she had to say passed comfortably over my head, but the gist of it, if I’ve got it right, seemed to be as follows:

The cross-section of a helicopter blade, according to Sarah, is more or less the same as the wing of an aeroplane. Its shape creates a pressure differential in the air passing over its upper and lower surfaces, producing a consequent lift. It differs from an aeroplane wing, however, in that when a helicopter moves forward, air starts passing over the blade that’s coming forward faster than it passes over the blade that’s going backwards. This produces unequal lift on the two sides of the helicopter, and the faster it goes, the more unequal the lift becomes. Eventually the ‘retreating’ blade stops producing any lift at all, and the helicopter flips on to its back and drops out of the sky. This, according to Sarah, was a negative aspect.

‘What the Mackie people did was put two rotors on a coaxial shaft, spinning in opposite directions. Equal lift on both sides, possibility of nearly twice the speed. Also, no torque reaction, so no need for a tail rotor. Smaller, faster, more manoeuvrable. It’s likely this machine will be capable of over four hundred miles an hour.’

I nodded slowly, trying to show that I was impressed, but not that impressed.

‘Well, fine,’ I said. ‘But the javelin surface-to-air missile will do damn near a thousand miles an hour.’ Sarah stared back at me. How dare I challenge her on this technical stuff? ‘What I mean is,’ I said, ‘things haven’t changed that much. It’s still a helicopter, and it can still be shot down. It’s not invincible.’

Sarah closed her eyes for a second, wondering how to phrase this so that an idiot could understand.

‘If the SAM operator is good,’ she said, ‘and he’s trained, and he’s ready, then he has a chance. One chance only. But the point of this machine is that the target will have no time to prepare. It’ll be down his throat while he’s still rubbing the sleep out of his eyes.’ She stared at me hard. Now have you got it? ‘Believe me, Mr Lang,’ she continued, punishing me for my insolence, ‘this is the next generation of military helicopter.’ She nodded towards the photographs.

‘Right,’ I said. ‘Okay. Well then, they must be jolly pleased.’

‘They are, Thomas,’ said Woolf. ‘They are very, very pleased with this machine. Right now, the guys at Mackie have only one problem.’

Somebody obviously had to say ‘which is?’

‘Which is?’ I said.

‘Nobody at the Pentagon believes it will work.’ I pondered for a while.

‘Well can’t they ask for a test ride? Take it round the block a few times?’

Woolf took a deep breath, and I sensed that, at long last, we were approaching the main business of the evening. ‘What will sell this machine,’ he said slowly, ‘to the Pentagon, and to fifty other air forces around the world, is the sight of it in action against a major terrorist operation.’

‘Right,’ I said. ‘You mean they’ve got to wait for a Munich Olympics to come along?’

Woolf took his time, drawing out the punchline for all it was worth.

‘No, I don’t mean that, Mr Lang,’ he said. ‘I mean they’re going tomakea Munich Olympics come along.’

‘Why are you telling me all this?’

We were on to the coffee now, and the photographs were back in their folder.

‘I mean, if you’re right,’ I said, ‘and personally I’m stuck in the middle of that "if" with a flat tyre and no spare - but if you’re right, what do you plan to do about it? Write to theWashington Post? Esther Rantzen? What?’

Both the Woolfs had gone very quiet, and I wasn’t absolutely sure why. Perhaps they’d thought that just laying out the theory was going to be enough - that as soon as I heard it, I’d be up on my feet, sharpening the butter dish and shouting death to arms manufacturers - but for me it wasn’t anything like enough. How could it be?

‘Do you think of yourself as a good man, Thomas?’ This was from Woolf, but he still wasn’t looking at me. ‘No, I don’t,’ I said.

Sarah looked up. ‘Then what?’

‘I think of myself as a tall man,’ I said. ‘As a poor man. A man with a full stomach. A man with a motorcycle.’ I paused, and felt her eyes on me. ‘I don’t know what you mean by "good".’

‘I guess we mean on the side of the angels,’ said Woolf. ‘There are no angels,’ I said quickly. ‘I’m sorry, but there aren’t.’

There was a lull, while Woolf nodded his head slowly as if conceding that, yes, that was a point of view, it just happened to be a massively disappointing one, and then Sarah sighed and got to her feet.

‘Excuse me,’ she said.

Woolf and I scrabbled at our chairs, but Sarah was halfway across the restaurant floor before we’d managed to get any meaningful standing-up done. She drifted over to a waiter, whispered something to him, then nodded at his reply and headed towards an archway at the back of the room.