They both refused my offer of tea or coffee. They sat side by side on my sitting-room sofa, with me perched forward in an armchair opposite. I felt unreasonably nervous. Gupta had an iPad. She would be taking any notes that needed taking. It was clear from their body language that Unwin was the boss.

‘Thank you very much for seeing us, Mrs Curtis,’ she began.

It wasn’t one of those ‘Call me Ellen’ moments, so I just said, ‘No problem.’

‘You were extremely helpful during our first conversation and there are a few details of what we discussed then that I’d like to explore further.’

‘Fine.’

‘I’ve explained to Detective Sergeant Gupta how you came to be involved with Ingrid Richards, how you were assessing the fire risk at her premises.’

That wasn’t entirely accurate but not worth arguing about.

‘I’ve also told her it was your view that the deceased was aware of the danger, but you thought she could manage the risk.’

Again, I could have taken issue about the detail but didn’t.

‘All of which would be fine,’ Unwin continued, ‘had the situation remained as it was when we last spoke. But we do now have different information. We have the results of the post-mortem on Ingrid Richards’ body and they reveal that, as well as a lot of Jameson’s whiskey, she had ingested sleeping pills that evening. Zopiclone, to be precise. The pathologist could not be certain but, from the residue found in her stomach, he got the impression that the pills had been ground up, presumably for ease of swallowing with a drink.

‘Now, this news does rather change our perspective on the case.’ She could say that again. My mind was instantly buzzing with new possibilities, but I didn’t think it was the moment to say anything, as she went on, ‘While it does not rule out accidental death, it does also open up the possibility of suicide … or even foul play.’

Detective Sergeant Unwin focused her small eyes on me. ‘So, Mrs Curtis, when you visited Ingrid Richards, did she by any chance mention whether she was in the habit of using sleeping pills?’

No difficulty with my answer. ‘She did actually bring up the subject, yes.’

‘And what did she say?’

‘She said that the life she’d led, the stress she’d been under in conflict zones throughout her adult life, meant that she could sleep anywhere. In fact, she said: “I’ve never had any need of sleeping pills.”’

This brought a gasp from Detective Sergeant Gupta, followed by a look of reproof from her senior. In the police force it was unprofessional to betray such instinctive reactions.

‘You’re absolutely sure about that, Mrs Curtis?’ asked Unwin.

‘Those were her exact words.’

‘Hm. Interesting.’ The two sergeants exchanged a look. ‘Particularly interesting because Ingrid Richards’ daughter told us this morning that her mother had been taking Zopiclone for years.’

Things didn’t look good for Alexandra. What she had told me about staying in her car in Brunswick Square after seeing Ingrid on the evening of her death seemed deliberately to have ruled out the possibility of anyone else visiting. At least till after midnight.