‘I didn’t see anything! I mean, I didn’t see anyone go in or come out, if that’s what you’re getting at, Mr Hawthorne. Even if I had looked out of the window – and I didn’t – it would have been too dark to see the bottom of the garden.’ She paused. ‘I think I did notice that the lights were on inside, but that’s all I can tell you.’ She was almost daring him to challenge her. ‘Is there anything else?’

‘Did you hear anyone come upstairs? During the party or immediately afterwards.’

‘No. Who would have come upstairs? Only Charles, and he didn’t, did he?’ She reached forward and stubbed out her cigarette. When she looked up again, there were fresh tears in her eyes. ‘And now we know why.’

Hawthorne took pity on her. ‘Thank you, Mrs le Mesurier. You’ve been helpful. There is just one last thing. Was your husband left-handed or right-handed?’

‘Why would you want to know that?’ She shook her head and sighed. ‘He was right-handed.’

‘Did he wear his Rolex on his right wrist?’

‘Yes.’

‘And do you know where he got it?’

‘He bought it in Hong Kong. It was gold – and very expensive.’

‘How expensive?’

‘He told me he’d paid £20,000, but it might have been more. Why do you want to know?’

‘The watch has gone. Do you know if he was wearing it last night?’

‘Of course he was. He never took it off.’ She corrected herself. ‘Only sometimes . . . before he went to bed.’ She looked uncomfortable. ‘He’d do that as a signal.’

‘What sort of signal?’

‘When he wanted to be intimate, he took off his watch.’

Hawthorne considered this. ‘But he didn’t come to bed.’

‘Not with me.’ She reached out and picked up her cup of tea as if to say that she’d had enough of these questions and wanted to be left alone. Hawthorne examined her for a moment. Then, with a nod, he left. Colin Matheson and I followed.

‘The office . . .’ Hawthorne said, as we stepped outside.

Matheson looked at him blankly.

‘I want to see where the paperknife came from.’

‘Oh, yes . . . This way.’

He led us down a corridor painted white with a single dazzle of colour at the end: a photomontage of Charles le Mesurier done in the style of Andy Warhol. There was an open door beside it and the three of us went into a modern home office with lots of bookshelves but very few books. An angular black wooden desk dominated the room. Buy two and put them together and you could have made a swastika. A black leather chair with a high back stood behind. A gleaming chrome desk lamp – possibly Italian, certainly expensive – curved towards a giant computer screen. A mobile phone, presumably le Mesurier’s, lay to one side. Using a handkerchief, Hawthorne picked it up and examined it. He showed it to me.