Holland had also faced repeated questions from Michael Finney about Pipistrelle. He had scolded Knox for revealing the name of one of MI5’s most important secrets to the CIA, but he also enjoyed seeing Finney squirm, aware that British intelligence had some sort of trick up their sleeve he knew nothing about.

The two men who had attacked Knox in Strand station and the man who had tried to assault Bennett in Hyde Park had been picked up by the police shortly after their identikit descriptions had been drawn and circulated. They’d all identified Peterson when they were shown his photograph. But none of them admitted to knocking Knox out in Kemp House, or being part of the masked team that had kidnapped Valera in Stockholm.

Knox’s first job once he’d been discharged from hospital was to work out just how badly Peterson had compromised MI5 over the years. The answer was, it seemed, mercifully little.

The Service had been very lucky. Knox combed through all of MI5’s most important operations over the last decade, as well as intelligence supplied by MI6 about Russia’s activities over the same period. He couldn’t find any major strategic decision or tactical move by the Soviet Union or operational problem that could be attributed to a KGB mole at the heart of British intelligence. In fact, it had taken getting access to Peterson’s bank accounts to establish when he’d started working for the Russians.

As Peterson had made clear to Knox as he stood over him in the suite in the Richmond, he wasn’t an ideological traitor. His relationship with the KGB had been strictly based on remuneration, and they’d paid him very well over the years for very little return. Peterson hadn’t left a record of exactly what he’d passed on to Russia, but by cross-referencing the timings of his second salary Knox was confident in his conclusion that the KGB had either ignored or chosen not to act on whatever information Peterson had given them.

The only loose end that still worried Knox was the ghost of Cecil Court. Even after she’d been sentenced, Sandra Horne had refused to confirm if it had been Peterson who had been helping the Calder Hall Ring. Knox couldn’t tell if she was trying desperately to hold on to one last sliver of power, or if she was bluffing and actually had no idea who the mysterious contact had been. Holland was happy to leave this particular thread dangling so it could be pulled on in the future if needed.

After Knox had completed his report and compiled a list of on­going operations that should be closely monitored just in case the KGB knew about them, Holland insisted that he take a holiday.