We stood together for a moment outside the Bar Italia and I could feel her disappointment. Had I really given her the impression that I was interested in her as something more than an informant? All I had done was show her some respect and kindness in a place where there was none.

And perhaps that was enough.

‘You have somebody else,’ she said.

‘I have an Irish lady who lives nearby who looks after my daughter, my dog and my home.’

I didn’t even know why I was telling her this stuff. Somehow I felt I owed it to her.

‘That’s not what I mean. You know what I mean. You have somebody else.’

I laughed at the idea. But she wasn’t laughing. She smiled sadly and I felt a flood of sympathy for her. She was trying to be a decent woman in a universe that was only interested in her when she was wearing a thong.

‘Where will you go, Bianca?’

‘Not Ilford!’

I held out my hand and she shook it, and that was when I saw the livid red marks on her wrists. Now she tried to take her hands away from me. But I would not let her.

‘Are they cigarette burns, Bianca? Who did this to you?’

She pulled her hand away, shaking her head.

‘No,’ she said. ‘No more white knights. No more pretending you will save me.’

‘Bianca—’

‘No.’

She turned up her collar and began walking north towards Soho Square. Already she looked like someone I had never met in my life. But then I had never seen her in daylight before.

I knew immediately.

I knew because MIR-1 was crowded with officers from every department in West End Central and they all had that look on their face.

It could have been me.

Here was the reminder of the knowledge that every police officer lives with, the terrible knowledge we do our best to ignore – the awareness that you might not actually be going home at the end of your shift, but to a hospital bed or a stainless steel slab in the morgue.

So I knew, and I felt that knowledge as a physical knot of grief and rage inside me, as real as a tumour, and it was in my gut and growing as I pushed my way into MIR-1, pushing too hard so that some of them looked up angrily and then looked away quickly when they saw it was me.

And I knew because I saw that DCS Elizabeth Swire was there, the Chief Super from New Scotland Yard, that this was big enough and bad enough for her to clear her schedule and come over from Broadway to Savile Row, and she was going to say something because somebody always has to say a few words when one of us is killed.