‘He looks like a nice lad.’

‘You cannot understand a mother’s grief if you have not experienced it. It tears the soul into shreds, hour by hour, day by day, week by week. His father abandoned us a year after Robert disappeared. But a mother has to keep going, to bear the daily pain of waking and recollection, for all eternity, to be there with open arms. Just in case.’

Gillard nodded. He’d seen too many such cases over his career. No mother ever truly recovered.

‘On the first anniversary of Robert’s disappearance, I took to my bed. I told my two remaining children that I would remain here in this room, until he was found, or until I could touch his forehead and bless him on the journey to the great beyond. I would eat, but would not go out into the cruel world that had taken him from me.’ Her voice broke, and she reached again for the oxygen mask. It was a couple of minutes before she was able to continue.

‘You look at me, and I see disgust in your eyes.’

‘It’s not what you look like, Mrs Tilling, it’s what you have done. You could have chosen another path.’

‘But eating, in my confinement, is my only remaining pleasure.’ She laughed, a high tinkling sound quite at variance with the body it came from. ‘Don’t you understand, Detective Chief Inspector, even now? I am grief, made flesh. Only when you see how much of me there is, only when I have been weighed on the scales of anguish, can you measure the depth of pain from which it all comes.’

Gillard turned off the light, closed the door and returned downstairs, having made only a cursory inspection of the woman’s room. For now he was stumped. This was a woman who could never manage to be a fugitive from justice, or indeed from anything. He could return when he had more information. He was clearly going to need help from medical professionals.

All the computer equipment had been removed from Tilling’s home office and was being ferried in large plastic bags out to waiting police vehicles. ‘What have you got?’ Gillard asked Rob Townsend, indicating the stack of plastic-bagged laptops and computers.

‘It’s too soon to say,’ the research intelligence officer said. ‘He really knows his stuff. A lot of his devices have very strong passwords, but we were lucky to catch one laptop that hadn’t yet shut itself down. So we might be able to find out what we need.’

Gillard beckoned Hoskins outside so that he could talk.

‘Has Gary Tilling said anything?’

‘No. He claims to know nothing about our Dr Chen. But we’ve got his mobile phone now, and we’ll be able to check. There is also a satnav in his car, so we should be able to double-check his movements.’