‘That’s Fort Baba Vida,’ Billy said. ‘Main tourist attraction of Vidin, Bulgaria. There are six more photographs, but I can’t identify the other locations. And the one in Vidin is the only picture that’s not a selfie.’

Billy began scrolling through the photographs. They told the story of a man and a woman, travelling across Europe, strangers who became intimates. It was only the first photograph that featured any attempt to capture a picturesque background. The rest of them seemed to be taken at a collection of petrol stations. But as the seven photographs progressed, the couple became more familiar.

‘Besser denn je!’ said a sign behind them in the last image, with the woman calling herself Rabia Demir snuggling in the arms of the man travelling as Zlatko Draganov. Now they were both smiling.

‘Better than ever!’ I translated. ‘So that’s Germany or Austria.’

‘And what happened to her, Max?’ Whitestone said.

‘He might have killed her,’ I said. ‘When he got to London and found he had a cargo of dead and dying in the back of his lorry because he was too stupid to think about controlling the temperature in a refrigerated lorry. Because he didn’t know how the thermostat worked. Or because – my guess – it never even crossed his mind that those women were in danger of freezing to death until he parked in Chinatown and it was far too late. Rabia Demir – the girl who got to ride in the cab – was a witness. If she talked to the law she could put him away for a long time.’

‘But only if she knew,’ Whitestone said. ‘And only if she saw. She was a passenger. A favoured passenger, no doubt about it, the passenger who got to sleep with the driver, but my guess is that she didn’t know what was in the back of that lorry. Because why the hell would he tell her?’

We were all silent, weighing the possibilities.

‘Whatever happened when he got to Chinatown, he was in a state of panic,’ I said. ‘If he killed Rabia and ran because she had seen too much, then her body would have been there.’

‘It’s possible he could have killed her and taken the body elsewhere,’ Whitestone said.

‘Yes, but my gut feeling is – they both ran,’ I said. ‘They got to Chinatown, he clocked what had happened in the back of the lorry, and all the plans went out the window. Draganov may have killed those women accidentally – he had probably never seen a refrigerated lorry before – but he killed them. He wanted to put as much distance as possible between himself and all those dead girls. So they ran. And they ran together.’

‘Then she’s here,’ Whitestone said. ‘She’s the only woman who was in that lorry left alive.’

I nodded.