Kate didn’t bother to answer that. She had many problems. Suzy’s bruised ego wasn’t one of them.

‘At any rate,’ Suzy said, ‘it doesn’t change the question those files keep on asking.’

There was a long silence. ‘I just need a bit of time to think,’ Kate said.

But it was going to take more than that to force Suzy to withdraw: she leant back against the filing cabinet, as if settling in for the long haul. ‘Either someone is tipping them off as to your every move,’ she said, ‘or they’re actually tracking you.’

‘Perhaps they found a way to inject a microchip into me.’

‘Stranger things have happened.’

Kate glanced at her. ‘This is real life, Suzy, not the movies.’

‘You ever consider the possibility that this has been a setup from the very first moment?’

‘Of course.’

‘No, I mean, really, that they’ve planned every stage of it methodically: the original tip-off about the meeting on that yacht, the news that the former PM had cancer, conveniently true, the idea that the leading candidate to replace him was working for them and now, suddenly, the “proof” that it must be true in the form of a sex video.’

‘You’ve spent too much time listening to Ian.’

‘I mean, I know you have this great source and—’

‘How do you know that?’

‘Ian told me.’

Ah, so that was it. It shouldn’t have surprised Kate that Suzy had chosen to throw in her lot with Ian. That much had surely been inevitable.

‘Don’t you think it feels like a classic Moscow long play?’ Suzy asked. Now she was using some of Ian’s favourite language as well.

‘I’m tired, Suzy. Do you mind if we discuss this another time?’

‘I’m just trying to help.’

No, you are not, Kate thought. ‘I know,’ she said. ‘Thank you.’

‘What did the source you went to see tell you? I’m assuming he or she was the person who tipped you off in the first place.’

‘Our agent told me Mikhail’s account of what has happened to his father is accurate. I’ll be briefing the foreign secretary to that effect in the morning.’

Suzy gave her a thin smile. ‘I guess it’s your call.’

She slipped away into the darkness. And it was all Kate could do to stop herself punching her computer. But she couldn’t quite persuade herself to log off and go home. She stared at those pictures of the Empress leaving the quay in Istanbul in the middle of the night. Who had known enough to warn them? Sir Alan, Ian, Julie, Danny. That was it.

But only Julie could conceivably have tipped off the Russians about her trip to see Sergei.

Unless Sir Alan had guessed what she was intending to do.