‘I understand.’ The voice softened. ‘They used to call it the wilderness of mirrors. Remember Golitsyn.’

‘Remind me.’

‘Our master spy, the double agent inside the KGB. Finally, he defects – they are onto him, he says. When he arrives, he tells us we are penetrated from top to bottom. The head of MI5 is a KGB mole – even a future British prime minister is a place man for the Russians. The head of CIA counter-intelligence believes him, as does a faction inside MI5. For the next decade we can hardly move because we are so scared of our own shadow. In a game of deception, how do you know whose side anyone is really on? How do you see into a conscience? Into a heart? And it matters because lives can depend on it. Thousands of lives.’

‘What are you saying? There’s some kind of traitor at the heart of MI5’s operations against Islamist terror?’

‘I am not saying anything. It is you who has just said that.’

‘I’m sorry, Sayyid,’ said Morahan gently, ‘or whatever your name is – I can’t play this game.’

‘It is not a game.’

‘Investigating these matters is not within my terms of reference.’

‘It is. Look at them. Why did we once succeed? Why did we then fail? I do not know the answer. You raise the suggestion of treachery.’

‘What else then?’

‘Remember extraordinary rendition? What follows?’

‘Tell me.’

‘I cannot. You started your journey by hiring the woman. It is for you to decide whether to continue.’

Morahan looked through the car window from their darkened space across the broad tarmac of the park’s concourse. A figure wearing a beret was stubbing out a cigarette underneath a lamp. He whistled; a dog came running. ‘I think I should leave now.’

‘Yes.’ Sayyid turned on the ignition. ‘I will drop you somewhere less isolated.’

He started the engine, turned round and headed down Chelsea Bridge Road. At the roundabout south-east of the park, he circled twice, satisfied himself no one was following and retraced his route across the river. ‘Basic procedure,’ he said, ‘but better than nothing.’ Instead of going left onto the Embankment he continued to Sloane Square and crisscrossed the Kings Road, heading all the while in the direction of Morahan’s house. He stopped a few hundred yards short of it.

‘We will not meet again.’ He continued to look rigidly forwards. ‘One final word. There is a destination. It is called Operation Pitchfork. I tell you this, but you must not allow any other to know you have heard this word. Not even the woman. At least not yet… if ever. That is too dangerous for you and her. And me. Take care of her. And of yourself.’