Potential threats to Joanna: first up, rival energy companies who knew she was Saracen-connected and wanted to stop the company’s expansion. Less likely: activists who’d rumbled her cover and felt aggrieved. Then there were always local political thugs who bought into the cover and might not have liked Vanessa McDonald nosing around. One long-shot involved individuals whose feathers she’d ruffled in the course of her MI6 career and who had chosen their moment to exact revenge. There was the possibility she’d been thrown to them by colleagues for whom she had become inconvenient; there’s always someone who’ll do your dirty work for you. It would have been quicker to establish those who didn’t want to kill her.

I watched some of the documentary footage she’d shot. She interviewed off-camera so I was denied her face. Still, I heard her voice. She interviewed a guy called Craig Bryant. He was a subcontractor for Saracen; his company, Auracle, had been bought up by Carter around the time he purchased the oil company. It provided tech support for rigs and pipelines. He sat in a bland office with some data pinned to the wall, looking awkward, ingratiating, played. He hadn’t expected criticism, starting out on his pitch:

… You’ve got a thousand kilometres of pipeline – no human’s going to be able to monitor …

Then, when she started throwing around stats on environmental destruction and political corruption he spent some time trying to convince her it was all more eco now and he didn’t know about politics.

According to her reports, in the following weeks they went on some dates. You could see from phone records that he’d been trying to call her since she went missing.

‘That’s bold. She interviews him and he asks her out.’

‘Plucky. But it seems he’s that kind of guy. Skirt chaser.’

‘You’ve looked into him?’ I asked.

‘Superficially. He’s American, born Sandpoint, Idaho, MIT grad, worked in technology all his life. Been dropped in by Carter to manage drone operations over here. He’s done some consultancy work for the NSA and spoken a couple of times at CIA-related organisations like the Brookings Institution, but that’s the extent of it as far as we can tell.’

‘Know what exactly these drone ops involve?’

‘They have high-end sensors – optical, chemical – which help with maintaining pipelines, detecting any leaks or pollution, assessing reserves.’

If Bryant struck Walker as worth pursuing, he didn’t show it. I searched through the notes on their investigation so far. There were her recent ATM withdrawals, card payments. The repetitive, unenlightening interviews with hotel staff. A copy of her itinerary as Vanessa McDonald, making her documentary.

I looked through for the detail that could help me and saw nothing.

Then I found it.