‘What do I know about Mrs Vanderlyn? I know that she’s an American subject. I know that she’s had three husbands, one Italian, one German and one Russian, and that in consequence she has made useful what I think are called “contacts” in three countries. I know that she manages to buy very expensive clothes and live in a very luxurious manner, and that there is some slight uncertainty as to where the income comes from which permits her to do so.’

With a grin, Sir George Carrington murmured:

‘Your spies have not been inactive, Charles, I see.’

‘I know,’ Lord Mayfield continued, ‘that in addition to having a seductive type of beauty, Mrs Vanderlyn is also a very good listener, and that she can display a fascinating interest in what we call “shop”. That is to say, a man can tell her all about his job and feel that he is being intensely interesting to the lady! Sundry young officers have gone a little too far in their zeal to be interesting, and their careers have suffered in consequence. They have told Mrs Vanderlyn a little more than they should have done. Nearly all the lady’s friends are in the Services—but last winter she was hunting in a certain county near one of our largest armament firms, and she formed various friendships not at all sporting in character. To put it briefly, Mrs Vanderlyn is a very useful person to …’ He described a circle in the air with his cigar. ‘Perhaps we had better not say to whom! We will just say to a European power—and perhaps to more than one European power.’

Carrington drew a deep breath.

‘You take a great load off my mind, Charles.’

‘You thought I had fallen for the siren? My dear George! Mrs Vanderlyn is just a little too obvious in her methods for a wary old bird like me. Besides, she is, as they say, not quite so young as she once was. Your young squadron leaders wouldn’t notice that. But I am fifty-six, my boy. In another four years I shall probably be a nasty old man continually haunting the society of unwilling debutantes.’

‘I was a fool,’ said Carrington apologetically, ‘but it seemed a bit odd—’

‘It seemed to you odd that she should be here, in a somewhat intimate family party just at the moment when you and I were to hold an unofficial conference over a discovery that will probably revolutionize the whole problem of air defence?’

Sir George Carrington nodded.

Lord Mayfield said, smiling:

‘That’s exactly it. That’s the bait.’

‘The bait?’