As soon as the rain had ceased, Patrick had insisted they move on; they were now on the Albert Embankment riverside pavement heading towards Lambeth Bridge where, he said, they would cross the river and complete the circuit. Sara was unsure whether Patrick’s ‘passing the police station’ theory was invention, convenience or learnt expertise. As his route took in MI6, the approaches to the Houses of Parliament and MI5, it was certainly thorough. Perhaps the real reason, which he’d left unstated for her sake, was that safety was best found in high-profile public places. None of this stopped her regularly looking around and behind; nor, she noted, did it stop him.

‘A contract,’ she repeated more softly. ‘For a man who, by his own admission, would be found guilty of terrorist conspiracy in a court of law.’

‘Yes,’ said Patrick. ‘But he was canny. He must have seen how much they wanted him. J would have played it cool, but I wondered at the time whether Isobel Le Marchant had betrayed desperation.’

‘To beat the bombers or get herself to the top?’

‘That’s unusually cynical of you, Sara. She’s a woman in a man’s world and she’s made it. Dame Isobel Le Marchant, Director General of MI5.’

‘Not the first one though,’ said Sara. ‘Or even the second.’

‘Quite so. After they’d allowed it twice, how much harder it must have been for her to complete the hat-trick. She would have needed constant success.’

‘But we don’t know what that “success” was. Or what Kareem’s job was to be.’

‘No.’

‘We have to assume that all Sayyid’s clues and information connect,’ said Sara. ‘So he’s operating out of some kind of interrogation base as “the Adviser”. And the Blackburn files are a window into it.’

‘Yes,’ agreed Patrick. ‘Glimpses. But no more. No sense of the scale Sayyid’s suggesting. Or where his activities – whatever they precisely were – end up.’

‘No. We’ve lost Morahan, we’ve almost certainly lost Sayyid too. Maybe we’ve lost ourselves.’

Before Patrick had time to respond, her mobile rang. ‘Hello… Are you there? Who is this?’

She shot a puzzled look at Patrick, shaking her head. She jerked up, on instant alert, marching forward in excitement, Patrick the one now keeping up. ‘Yes, Mrs Green… She really does, does she?… You think straightaway… tomorrow, yes, I’ll come, I’ll change plans… Thank you, I’ll jot it down…’ She gestured to Patrick to pass her pen and paper and began frantically to write. ‘Yes, I understand, I’ll try not to… Midday tomorrow then… Thank you so much, Mrs Green, goodbye.’

She put the phone away, buried her face in her hands and stopped in her tracks, leaning against the railings overlooking the river. Patrick waited for the seconds to pass. ‘I heard breathing. It felt like a woman. Then her mother took the receiver.’

‘Hold on, Sara. Who?’

‘Marion. Maryam.’