My belongings were returned, although the gun had no bullets. I was led out. Glukhovka was pretty much just a crossroads, with a petrol station, the restaurant and not much else apart from six blacked-out armour-plated SUVs scattered across the frozen mud.

One of them took me to Semey. Two men sat up front, with an AK-47 propped between them. The driver chainsmoked, glancing in his mirror at me then looking away instantly when our eyes met. The dashboard clock said 8 a.m. We drove back into barrenness: snow and rock. I checked my bruising in the rear-view mirror. I looked rough.

Block 9 was a supergiant, the largest class of field, with 1 billion or more barrels of ultimately recoverable oil. Fewer than forty had ever been found, and two-thirds were in the Persian Gulf. People hunted hard, but for years the word was that there were no more out there. I did the maths. Even if the estimates were optimistic, it was vast. Thirty trillion cubic feet of gas, 5.5 billion barrels of oil: that would meet Europe’s energy needs for years to come. All buried 50 miles from the Russian border.

I messaged Walker with an update and he rang back. ‘We got a call from Akan Satayev.’

‘What did you say?’

‘We told him not to kill you. What took you east?’

‘Block Nine, it turns out. You didn’t mention it.’

‘It’s incredibly sensitive. Are you able to get here?’

‘I’m sure I’ll find a way.’

The more oil around, the less I trusted people, and my trust levels had been minimal to start with. But the hardest question was whether you could trust yourself. I thought through the exchange with Satayev and felt the ice of Christopher Bohren hardening around me again.

I fell asleep, and when I woke Semey was visible on the other side of the Irtish river. Ten a.m. on the dashboard. The town looked innocent enough, in the way of medium-sized towns: snow-crested, a scatter of older buildings among the concrete, arranged between the river and the mountains behind. A suspension bridge crossed the river towards it. Population 300,000. No sign that twenty of them had been shot dead in the last forty-eight hours. I wanted to assess which way the wind was blowing. Whether they were ready to join Russia, who was steering this, how far they were prepared to go. Call it habit.

We crossed the bridge, above lumps of ice floating downstream. The town was called Semipalatinsk until 2007: seven-templed city, named after the ruins of a Buddhist monastery. By the time they decided it was time for a rebrand the name meant nothing but nuclear tests. I’d met a nurse in Moscow who used to work in Semey’s central hospital and remembered terminally ill children running around the wards pretending to be radiation.

Now Semey was metamorphosing again.