While Dyer considered his reply, her hand rose to her throat and toyed, as if to see it was still there, with a thin silver chain around her neck, like his mother’s necklace that brushed his cheek when she bent to kiss him goodnight. Like Katya’s. What a disaster that had been.

‘I’ll fetch your tickets,’ said Miranda, playing along. She got up from the table and disappeared. When she came back, she was clutching the brown envelope that Dyer had addressed to himself, containing the eleven pages of his conversation with Marvar.

The old lady was combing her hair in silence.

‘It’s all right, you don’t have to tell me,’ Miranda said, ignoring her.

But he wanted to. ‘It’s the explanation to a problem, the background to it.’

She looked at him diagnostically. ‘A big problem?’

‘You could say that.’

‘An explanation that others would itch to get their hands on?’

‘More or less.’

‘Without which the problem stays a problem?’

‘Yes.’

That was it, he realised. No one would understand the significance of Marvar’s algorithm without reading Dyer’s notes. The one depended on the other. The two documents were bound inextricably. Like Dyer and Marvar.

‘And who’s it for?’ she asked. ‘This explanation?’

‘I still haven’t made up my mind. I first wanted to check it was safe.’

It was pitiable, he was backtracking already. Just when he’d hoped to disentangle himself by destroying his notes, Miranda showed him that this was impossible. For Dyer to wash his hands of what he had written would be to flush Marvar’s algorithm down the same sink. He would have to destroy them both. Or neither.

She nodded at his dilemma, she saw it in his moping cod expression.

‘You can leave it here if you like. Until you’ve decided.’

He was regarding her. Her tanned face was in profile. She had seemed a little dowdy, perhaps it was her hair. He was thrown off balance by her without knowing why.

Her mother was still combing. She did not glance up or say anything when Dyer rose from the table, gathered his shoulder bag.