Of course, some people wanted a closer look at the destroyer, and a plan was hatched between MI5, MI6, and Naval Intelligence to do just that. There was a rumour that the Surcouf had a new underwater guidance and torpedo detection system installed on the underside of its forward hull, and the navy wanted to know if it really existed before they made overtures about an official exchange of information.

Knox was put in charge of the mission, and Williams, who had spent six months training with military divers for exactly this kind of operation, led the dive team.

The night that de Gaulle was in London being wined and dined at Buckingham Palace, the clouds over Southampton were thick and the harbour water dead calm—perfect conditions for a clandestine dive.

Confidence was high as Williams and his team slipped into the sea outside the harbour and made their way towards the destroyer. But when all the divers but Williams surfaced on time, Knox became concerned. When he hadn’t appeared after twenty minutes, concern turned into worry. Williams had enough air in his tank to last an hour, but that window came and went with no sign of him. This was the one outcome Knox hadn’t prepared for. He ordered people to comb both sides of the Southampton estuary all the way up to the Solent. They found nothing. He wanted to send every diver back into the water, requisition boats to start dredging the harbour. But by then it was morning, and doing either would make it obvious to anyone within fifty miles that Britain had been flagrantly spying on an ally in the middle of a state visit. So, nothing was done.

The next day Williams was quietly listed as missing in action, and the operation, which had only proved that the guidance and detection system was just a rumour after all, was officially forgotten.

Without his closest friend, and racked with guilt over his death, Knox started to unravel. While his colleagues may have only seen his usual professional mask harden, Holland could see cracks starting to show in it. He arranged for a short leave of absence after the painful debriefing at which Knox was absolved of any responsibility for Williams’s unfortunate but accidental death. And when the leave ran out and Knox didn’t return to Leconfield House, Holland went looking for him.

He found him in the Gresham Arms, unshaven, unkempt, and cradling his fifth pint of the day. Holland sat down opposite Knox, lifted the pint glass from his hands, and told him that this wallowing wasn’t doing anything to respect Williams’s memory and that he needed to pull himself together and get on with his job.

The next day Knox was back at headquarters, and the following week Sarah Holland arranged a small, private memorial for Williams.