Holland looked at Knox, then Williams, then his wife. After what felt to Knox like a long and damning silence, he strode over to Williams, shook his hand and said, ‘Welcome home.’ Then he turned to Knox and added, ‘we need to talk.’

Sarah took her cue and tempted Williams out of the room with the offer of a cup of tea. Williams, visibly relieved by Holland’s reaction, followed her.

‘It’s really him, then,’ Holland said once he and Knox were alone.

‘It is,’ Knox replied.

They moved to the twin high-backed chairs next to the fireplace. Low, flickering flames produced the odd quiet pop and crack.

‘It didn’t take you long to catch up with him,’ Holland said. It was clear from his tone he knew Knox had lied to him in Leconfield House, but also that he understood why.

‘Me and a couple of other people,’ Knox said.

‘How was that?’

‘It turned out worse for them.’

Knox told Holland about the unexpected appearance of the two men he hadn’t been able to identify, and their equally surprising deaths. He also finally told Holland about the attack Williams had mentioned in Regent’s Park.

‘I haven’t got any concrete details out of him so I don’t know how legitimate the threat is.’

‘Or if it’s a memory of an old operation,’ Holland said. ‘Or simply a figment of a fevered imagination.’

Holland’s conclusions were among the possible ones Knox had also reached—he knew there’d been plenty of times in the war, and after, when Williams had been involved in life-or-death missions that could have become jumbled in his head—yet hearing someone else dismiss Williams’s warning instinctively compelled him to defend it.

‘I think we should take what he’s telling us seriously,’ he said.

‘We will,’ Holland replied. ‘When he’s fit to be debriefed.’

‘What if we don’t have time for that?’

‘No verified intelligence has indicated any imminent threat to London, or anywhere else in the country for that matter. I can’t make decisions based on one sentence from someone who isn’t in their right mind.’

‘He’s still an MI5 officer,’ Knox said. ‘He’s earned our faith, and he’s our responsibility.’

‘I’m fully aware of all my responsibilities, Richard. But he’s now proven he’s dangerous, and as soon as he steps inside Leconfield House the Americans will get wind, register a formal protest and create exactly the kind of incident I’ve been told by the PM to avoid at all costs. He doesn’t want another Vassall or Profumo before the election. And he doesn’t want anything to derail the summit.’

‘This is different,’ Knox said. ‘This isn’t a double agent, or a minister who can’t control his libido.’

‘No, it’s one man’s confused words.’

‘It’s Jack Williams.’