If anything, Sir Alan’s career progression had been more predictable and solid – more conventional, perhaps – based on his unarguable social skills, emotional intelligence and steely resolve. His first foreign posting had been to Warsaw in 1988, where he had worked undercover in the Chancery section of the British Embassy. But he had then moved on to Prague in 1990 and Moscow in 1993, by which time he was the press secretary. There was a consistent pattern of reported recruitment of foreign targets in all these locations, though little subsequent reference to them. Were his successes less influential than Ian’s, or was the latter just better at blowing his own trumpet and making sure he got the credit?

Sir Alan was apparently brought back from Moscow early to serve undercover in Bosnia with the SAS. After that, he spent two years in London on the desk that covered Italy and Spain before being posted to Pretoria for three years as the declared (to friendly countries, at least) SIS station chief.

He had moved back to London as deputy head of the North America Desk before being posted to Washington as station chief. This had led to the Russia Desk and spells as controller of Europe, then Counter-Terrorism before he was made C.

Kate sat back. Was it her own personal friendship with this man that made him so much less likely a suspect? There was nothing here – nothing at all – to hint at any possibility that he might be working for a foreign power, but perhaps he was too clever for that.

Kate got up. A thick bank of cloud had darkened the skies outside, so it looked like night was already closing in. She glanced at a copy of her own personnel and vetting files on the far corner of Shirley Grove’s desk.

Surely that couldn’t be passed off as a box-ticking exercise.

She got her coat, carefully locked the door of the apartment and walked out into the spitting rain. It took her half an hour to get home. As she passed her mother’s nursing home by Battersea Park, she noticed that the light was on in Lucy’s window on the fifth floor. And, just for a moment, Kate thought she had glimpsed her mother’s face in the window, peering out into the gloom.

She did not go up to visit.

But the scene that confronted her at home presented different challenges altogether. Around the kitchen table sat Fiona, Gus and Rose. They were FaceTiming Stuart in Moscow. And Rose’s cautious welcome was warning enough. ‘Have you heard?’ Gus asked.

Kate dropped her coat into the armchair in the corner of the kitchen and glanced at Nelson, who rolled on his back in his basket, his own particular brand of welcome. ‘Heard what?’ Kate asked.

‘Fiona came to school this afternoon and filmed the trial for Dad. All of it! It was so exciting.’

‘He’s been made captain of the First Fifteen,’ Stuart said, beaming from the rectangular prism of their son’s phone. Either the colour was off, or he had covered himself with fake tan. He looked most peculiar.