“That’s the point. It became a very big question for us. When we saw what the Chinese had on American space defense, on Ptolemy, there was a lot of debate within Six about how to proceed. Protocol was to hand over to Washington, step discreetly away, lips sealed. But we decided that identifying the source of the leaks could give us some serious standing. And I knew that if we handed it over, we’d lose our chance. Done wrong and they’d go to ground, then the opportunity’s lost forever. If someone has managed to get that level of access, they’re exceptionally skilled, exceptionally well concealed. They’d been in place for years, which meant years of cover above them.

“So, we did our own search. We knew this depth of intelligence wasn’t the product of hacking. They had someone close to the program. And we put everything into establishing who they were. Was it possible there was a mole at the heart of the Pentagon? Could they be in the new Space Force itself? The problem was that Zhao had no idea, because the source wasn’t being run by the Chinese. New intel came in after high-level meetings in Moscow: China-Russia meetings. That changed things, but it made sense. We knew there’d been a Soviet unit dedicated to infiltrating the US space program right up until the collapse of the Soviet Union. China has the technical superiority now, but Russia still has the deep network of human assets. It looked like there was some kind of trade-off. So we began thinking along these lines. We redirected attention toward the Russian agencies, pulled in expertise from the Russia desk. That was when we started hearing about Gemstone.”

Latham eased himself away from the bench and they set off again, this time away from the river, deeper into woods.

“Back in 2011, the Russian desk had managed to bug a negotiation in Minsk between senior Chinese and Russian officials in which they refer to an asset by the codename Gemstone. From what was discussed it seemed Gemstone was a Russian spy, central to an intelligence-sharing arrangement. Russians needed access to Chinese space research. They could see the Chinese space program was going to overtake their own in a matter of years. But they had this card to play: an officer who could supply regular, detailed intelligence on Ptolemy.