We walked up and into the main living room, with the seating area on one side, a dining table in the middle and a kitchen at the back. The flat had been a meat warehouse a hundred years before and it still had an industrial feel with high ceilings, exposed brickwork and lots of empty space. I saw Cara taking in her surroundings and felt strangely violated, having her here. She hadn’t been invited. She had invaded.

‘Would you like to sit down?’ I gestured at the table. I wanted this to be businesslike and the sofas didn’t feel appropriate. Nor did I offer her coffee or tea. I still had no idea what had brought her here but I wanted her and her assistant out as soon as possible.

They sat at the table. ‘Nice place,’ Cara said.

‘Thank you.’ There was a long silence. I was standing by the grand piano – which I had inherited from my mother and which I played every day – and I realised that Cara was waiting for me to join them. I walked over and took my place at the end of the table, as far away from them as I could. ‘So …?’ I asked.

‘I wonder if you could tell us where you were last night?’

It was a line I would never have used in a television drama – it’s such an old chestnut – but that was really how she began.

‘I was in bed,’ I said.

‘Before that.’

‘I was at the theatre.’

Mills had already been scribbling my answers down in his notebook, but somehow he picked up the fact that he’d been given his cue. ‘It was the first night of your play,’ he said.

‘If you knew that, why did you ask me?’

He ignored me. ‘Mindgame at the Vaudeville,’ he went on. He twitched his moustache without seeming to move his upper lip. It was a neat trick. ‘It hasn’t had very good reviews,’ he went on. ‘The Guardian said it was pretentious.’

‘I don’t look at the reviews,’ I muttered.

‘The critic from the Daily Mail said it was the worst play he’d ever seen. The Times wasn’t sure. Variety said: “It’s so goofy it’s almost fun.”’ He looked at me sadly. ‘Almost,’ he repeated.

I felt the familiar sickness in my stomach. ‘It’s very nice of you to come and tell me what the newspapers think of my play,’ I said. ‘But wouldn’t you say that’s a slight waste of police time?’

‘And Harriet Throsby was the worst of all,’ Mills went on. ‘She really tore it apart. I imagine they’ll publish her review posthumously in the Sunday Times. Maybe they’ll frame it in a black border. That would be a nice touch, wouldn’t you say, ma’am?’

These last words had been addressed to Grunshaw. She nodded slowly.

‘Sort of a … final curtain,’ Mills added.

‘What are you saying?’ I cut in. ‘Is Harriet Throsby …?’ I couldn’t finish the sentence. Not because I was shocked. It just seemed so unlikely.