‘Precisely.’

She thought about this. ‘I don’t get it,’ she said.

‘Yes, you do.’

Kate flicked on through the file. The woman who had passed herself off as Katya had been assessed by SIS’s Bucharest station chief and rejected on the grounds of unreliability. ‘So she tried again,’ Kate said.

‘Yes. But what had changed in the meantime?’

‘Ian had requested an assignment on the Russia Desk, so was in a position to make sure that, this time, Katya – or Irina, or whatever her real name was – passed through the checks and on to our books.’

He got up again and returned to the desk. This time he brought a thick collection of green files and dropped them with a thump in front of Kate. ‘You’ve probably worked out by now that Ian went on to recruit a young assistant military attaché in Santiago, who is now General Menov, chief of the Russian General Staff.’ Sir Alan moved to the other side of the coffee-table and leant against the fireplace. ‘I’ve double- and triple-checked Menov’s material, which has remained strictly for eyes only controller, Europe, and C, and concluded each time that it was reliable and genuine.’

‘Menov was his calling card,’ Kate said.

‘Right!’ Sir Alan slapped the brick chimney, in a display of frustration or anger that was quite out of character. ‘We were all so dazzled by Ian’s product that we failed to see we were being played in the most old-fashioned way imaginable. Menov’s solid and genuine material bought Moscow two things: a guarantee that Ian’s career would continue to progress to positions of ever greater influence and power.’

‘And the certainty that any other material he brought to the table would be treated with the utmost seriousness,’ Kate said, finishing his train of thought.

‘Precisely.’ Sir Alan faced her again. ‘We were so impressed with Menov that we took our eye off the ball when it came to Irina’s material. If Ian vouched for it, it must have been kosher. Their misinformation plays were begun in earnest there and then. And we’ve been eating them up ever since.’

‘But why did Irina approach me?’ Kate asked.

Sir Alan sat in the chair again and stared into the empty fireplace. ‘I’ve been asking myself that,’ he said quietly. ‘The way it looks to me is this: they tried to get Irina on to our books in Bucharest, but didn’t have any luck. They recruited Ian in New York, then got him back to London to a position where he could make sure the next approach was taken more seriously. It would have set off red flags to produce her in London, so better to have her approach a busy young officer working in Counter-Terrorism in Istanbul, in the full knowledge you would have to pass it on to the Russia Desk in London.’

‘And once they’ve got it all set up,’ Kate said, ‘they give Ian Menov to act as his guarantee.’

‘Yes,’ Sir Alan said. ‘Yes.’