And perhaps their jobs were not all that different from the jobs of any others among the legions of civil servants who worked in London. They attended meetings, no doubt, wrote memos, and strove, he imagined, to meet targets. At the end of the day they probably went home in much the same mood as everybody else, leaving behind the cares of the office. He wondered if they had a clear-desk policy, as other organisations had, whereby there would be no papers left un-filed by the time work finished at five o'clock. He thought that they probably did; the sort of papers these people dealt with certainly could not be left lying about for the prying eyes of cleaners who might have been recruited by the other side. And it would be very easy, he reckoned, to recruit a cleaner; their weakness was tea, and they could doubtless be tempted by a large cup of Darjeeling …

He smiled at Angelica. “Well, I must say that I'm somewhat surprised. I've never met anybody who actually works there.”

Angelica returned his smile. There was nothing guarded about her manner; she seemed completely open and unembarrassed. “I know that it takes many people by surprise, but it's essentially an ordinary job. I don't really think about it, you know.”

“A daily grind like everything else?”

Angelica thought for a moment. “To an extent. A lot of what I do is pretty mundane, but there are times when things … well, when things hot up.”

William was intrigued. Did Angelica ever find herself in danger? He decided to ask her outright, and she shook her head. “I've never been in physical danger myself - as far as I know. But some of my colleagues have.”

William wanted to know more. “I suppose you can't say too much,” he said. “But can you give me an idea of what happened to these colleagues of yours?”

For a few moments Angelica appeared to be weighing the merits of saying more. “I have to be careful,” she said. “We're not meant to talk about our work, but …”