‘I suspect there’s no Muslim with the experience in the GLD. Plenty of younger ones coming up through the ranks – people are more aware of it now. So maybe there was an element of cack-handed “diversity”. Remember that Patrick is not entirely typical. He had educational advantages and prospects not available to many other young black men at that time and has reached a senior level ahead of them.’ He frowned. ‘Has something come up?’

‘No. Not really. It’s just that I sensed once or twice he’d almost prefer we didn’t find things than we did find them.’

‘I’m surprised to hear that. He was extremely keen to do it. As I understand, he put his hand up almost the minute the Inquiry was announced. And came warmly recommended by his superiors.’

‘Which superiors?’

He screwed up his eyes. ‘What a curious question, Sara. GLD, of course.’

‘Sorry, stupid of me.’

They exchanged smiles and fell silent. Despite her self-instruction to disregard them, she’d wondered whether to tell Morahan about the anonymous text messages; now that there’d been two, he should perhaps see them and there was no need to mention the 2005 text for him to take them seriously. Somehow, their exchange about Patrick made it the wrong moment. She would tell him next time.

He hoicked himself to his feet, at full stretch towering over her, and crossed the room to a window. ‘I wasn’t sure whether to confide something in you,’ he began, ‘and I’m afraid doing so may be more helpful to me than to you.’

She saw the other Morahan – the vulnerable man thrust into a strange unfamiliar world. ‘Please do.’

‘I have spoken with Sayyid.’

‘You met him? Face to face?’

‘Not quite.’ Propping on the window ledge, he explained the circumstances of the encounter – the sighting limited to the back of a covered head, the voice distorted – and described Sayyid’s mysterious remarks about the wilderness of mirrors. ‘I’ve since reminded myself of the details, you may not know them. It happened in the early 1960s. The Prime Minister Golitsyn pointed to as a Soviet sleeper was Harold Wilson. He was nothing of the sort, of course, but it didn’t stop his name being blackened and the intelligence services allowing suspicion and accusation to eat away at them.’

‘I don’t see how that could relate to Islamist terror,’ she said.

‘I know,’ he replied uneasily. ‘My curiosity about Sayyid’s arcane methods is leading to a sixth sense that somehow he is playing me. I’m the trout on the end of his fly as he slowly pulls me in.’

‘We can only deal in facts,’ she said softly. ‘Files, documents, witnesses, statements. Physical evidence if we ever find it.’