‘What do you make of that, Tony?’

There was a smear of something rust-coloured on the back. ‘Blood?’ I asked.

‘I think so.’

‘But how is that possible? If he was killed in the Snuggery, how did the phone get to be here?’ I thought it through. ‘Maybe it’s somebody else’s blood.’

‘We’ll have to get a test.’ He laid the phone down again.

The room was so neat and minimalist that it was impossible to tell if anything had been disturbed. Hawthorne said nothing as he opened three of the desk drawers – the fourth was locked – and tapped the computer to see if it was turned on. It wasn’t. There was another vibrant artwork on the wall, matching the one outside in both size and style. This one showed Helen le Mesurier standing beside a roulette wheel, holding a paddle. The face that launched a thousand chips.

‘I’m not sure we should really be here,’ Colin Matheson said.

‘Nobody’s asking you to be here,’ Hawthorne replied, affably.

He searched around, possibly looking for the key to the locked drawer, then gave up. There was nothing here. But at least he had established a sequence of events . . . or so I imagined. Whoever had killed Charles le Mesurier had come back into the house from the Snuggery and continued upstairs. They had searched for something in the study while Helen le Mesurier slept a few doors away. Perhaps they had picked up the mobile phone, transferring a bloodstain to the back. Could that even be the reason why he had been murdered? Was there something on the phone or the computer that the killer needed? Le Mesurier had been tied down. Perhaps he had been threatened with torture unless he gave up the password. Yes. That made sense.

We heard the front door open and Kathryn Harris’s voice coming from downstairs. She sounded indignant. That reminded me of what had happened the night before in the kitchen: Charles le Mesurier almost assaulting her. Quickly, I drew Hawthorne aside and told him what I’d seen.

‘If anyone had a motive to kill him,’ I said, ‘it was her.’

‘When was this?’ Hawthorne asked.

‘It was just after his wife had gone to bed.’

Hawthorne smiled. ‘At least he had the decency to wait until she was out of the way.’

We made our way back downstairs to the entrance hall. Marc Bellamy and Kathryn Harris had arrived together. He was looking very much the worse for wear, pale and dishevelled, as if he had slept badly. Someone had just woken him up, bundled him into a taxi and brought him here. I probably didn’t look much better.