Kate stared at her hands. How often had she asked herself this question? So much seemed to hang on it – and more with each passing day. ‘I think so, but it’s impossible to be sure without spending a little time with him. I’m going on a friendship of half a lifetime ago and the man I knew then. But people change. So . . . I don’t know.’

‘Has he been in touch with you since Stuart’s defection?’

‘Not until that exchange in Berlin.’ The waiter came with their food. Sir Alan tucked into his as if he hadn’t eaten for a week. ‘I could try to make contact again,’ Kate said.

‘I thought you said he wasn’t replying?’

‘I know where his parents live in St Petersburg.’

‘We could ask Andrew to send someone up. But it seems a long shot.’

‘I meant I’d go myself.’

He looked up at her sharply, his lunch forgotten. ‘I’ll pretend you didn’t suggest that, Kate.’

‘Just hear me out.’

‘No. It would be a ridiculous risk, which I couldn’t countenance and nor should you.’

‘It has to be me,’ she said. ‘They grew up in the old Soviet Union. They wouldn’t dream of talking to someone about their son unless they knew him or her.’

‘I’ll have a word with Andrew, see what he thinks.’

It was said with finality, but Kate couldn’t let go of the idea. It was against every conceivable current procedure and protocol for a senior serving officer to travel undercover into Russia alone. But C was right: everything that had happened had begun with Sergei and they would make no real headway until she could see him and get a sense of what his motive truly was. Meg Simpson had said she needed certainty, and Kate could see only one way to get it.

She pushed the food around her plate. Sir Alan stared out of the window. ‘There was one other thing,’ she said.

He faced her again. ‘Go on.’ Kate finished the last of her cod, though she wasn’t in the least hungry. ‘The suspense is killing me,’ he said.

‘I know what you’re going to say, but I do feel really strongly about it.’

‘The wrong sort of preamble for a successful negotiation, but never mind.’

‘When I recruited Lena Sabic to go and plant that bug on Igor’s yacht, I looked her in the eye and swore that, if she kept her side of the bargain, I would make sure we rescued her sister, Maja, from Belgrade, and brought her to this country.’

Sir Alan didn’t blink. ‘And we assuredly would have done so if Lena had survived.’

‘But that’s just it. Lena paid for this deal with her life, which, from my – from our – point of view, writes it in blood.’

‘Interesting use of terminology, which I don’t know that I accept.’