And Ian appeared to be a case in point. After New York, he had returned to a year on the Russia Desk at Vauxhall – the personnel file recorded he felt his Russian language skills honed at Oxford were getting rusty – during which period he had brought on board the agent Irina, whom Kate had passed on to him from Istanbul. And then, after a year’s immersive Spanish language training, Ian had been sent as the station chief in Santiago, Chile.

Why there? Well, this did and didn’t make sense to Kate. On the one hand, it was an out-of-the-way posting for an ambitious young intelligence officer – particularly one who had recruited his first foreign agent. But, equally, it was a promotion – and quite a big one. The Service had only opened the station in Chile three years earlier and was to close it shortly after Ian left, but not before he had used his few years there to achieve a triumph of which Kate had previously been unaware and which seemed to go a long way to explain his subsequent meteoric trajectory.

Because the file clearly recorded that, in Santiago, Ian had managed to recruit a source in the Russian Embassy who had, as subsequent assessments confirmed with growing praise, gone on to be a significant player in the Kremlin’s opaque power structure. The personnel file did not, of course, record whether the new recruit was in Russia’s diplomatic service, intelligence service, or military, still less his or her identity. But it was the start of something. After that, Ian’s career progressed steadily. He was posted to Berlin, Brussels and Paris – all plum assignments – with spells in London in between, before taking over the Russia Desk and eventually being appointed controller, Europe.

The files made only glancing reference to Irina, the translator in Istanbul, her recruitment and the debacle involving the German finance minister. It was clear that the agent in Chile – whoever he or she was – had made Ian’s career.

All of which begged so many questions. How come Kate, as head of the Russia Desk, had been entirely unaware of this agent’s existence? It was custom and practice for an agent’s identity to be a secret beyond the immediate handling team but, even so, she couldn’t imagine whom it might be, given the reporting out of Moscow that had crossed her desk.

Perhaps Ian had insisted the stream of information from this source came only to him after he was promoted to controller, Europe.

But there were other, equally pressing, concerns. Was Ian’s recruitment of this agent just luck? Had he used the kind of intelligence skills that were internally legendary to spot, track and recruit someone whose potential for treachery might not have been picked out by others? Or had he known that the source was there for turning before he left London for Santiago? And, if the latter, could it have been a set-up by Ian’s Moscow handlers to ‘make’ his career back in London and ensure that he was thereafter on an upward trajectory of ever greater force, with the access to more and more important secrets that flowed from it?