She set the mask aside. ‘Detective Chief Inspector,’ she said, her voice now at a more conventional register. ‘I have been confined to my bed for nearly thirty years. Whatever it is that you are investigating, I’m afraid I can’t help you.’

Gillard completed reading her rights.

‘Are you going to arrest me then? Drag me out of my sickbed? Squeeze me into a police car? Leave me overnight in a cell? The truth, Detective Chief Inspector, is that if I resisted, even ten of you couldn’t get me down the stairs.’

Gillard had no answer to that. She was right. The staircase was steep and narrow, obstructed even further by the stairlift screwed into the floor that was clearly far too insubstantial for this woman.

Her small deep-set eyes stared out at him from her fleshy face, like two currants from a bun. She gathered her hair up and tied it into a ponytail, the wobbling dough of her numerous chins flopping from one side to the other as she did so.

‘I can tell that you are repulsed by my appearance,’ she said. ‘Most people would be. But I wasn’t always like this.’

‘I remember. I met you, briefly.’ The wall was hung with framed photos, including a large studio portrait of a slender young woman with a 1980s-style perm.

‘That was another life,’ she said. ‘Before I got married, before I had any children, before my eldest son was murdered.’

‘Robert. Yes, we talked about him. I remember you from the public appeal, and the reconstruction.’

‘If you are investigating a murder, Detective Chief Inspector, let’s start at the beginning, with my son.’

‘The disappearance of your son has been investigated many, many times—’

‘Without result. Now it seems you prefer to persecute the victims of murder, the vulnerable and those with disabilities.’

‘I’m not persecuting you. I’m investigating two murders. Rollason, and a man called Dr Wei-Ling Chen.’

She said nothing, sucking on oxygen, her eyes boring into him.

‘Mrs Tilling, did you kill Dr Chen?’

‘I didn’t murder him, if that’s what you mean. He had terminal cancer. I helped him.’

‘The Charon Foundation sent him to you, didn’t they?’

‘That’s right. He was willing to pay a big woman to dominate him, to smother him. They tried a lot of the professional dominatrices, the so-called big beautiful women. They couldn’t find anyone who would go right through with it, to the ultimate conclusion.’

‘How did they find you?’

‘Through my mukbang channel.’

‘Your what?’

‘I eat, professionally. People watch me on the Internet.’

Gillard tried to hide his amazement. ‘Who pays you?’