Hawthorne had found something in one of the drawers. He was holding a camera, the sort used by sports enthusiasts, a GoPro Hero. It was remarkably small, no more than a couple of inches in height and depth. He was turning it over in his hands, working out how to activate it, and at that moment I realised its significance. Abbott had been blackmailing Colin Matheson about his affair with Helen le Mesurier. Colin had thought that there was a security camera recording what had taken place in the Snuggery, but Hawthorne and I both knew that wasn’t true. Was it possible that the footage had been recorded with this tiny device?

Hawthorne found the On button and pressed it. The answer to my question was apparent straight away. The little screen on the back flickered into life and there was the inside of the Snuggery in full colour, empty to begin with but almost at once Colin Matheson appeared. The camera had been concealed above the door. I saw his head and the back of his shoulders as he moved into the room and briefly disappeared out of shot. Helen le Mesurier, wearing a bright red dress that showed more flesh than it concealed, followed, carrying a bottle of champagne. She went the other way and sat down on one of the leather banquettes I had noticed when I had first gone in there. She placed the champagne on the table in front of her. Colin Matheson came back into view as he crossed over and sat next to her.

The bottle was already open. Helen filled two glasses that had been standing on the table. They talked, but there was no sound and because of the high angle it wasn’t even possible to read their lips. They kissed. The image was so small and the camera so far away that I couldn’t see the expression on Colin’s face, whether he was reluctant, embarrassed or passionate, unable to control himself. Paradoxically, the GoPro only gave me the bigger picture. The kiss became more intense. His hands slid under her dress, pulling it off her shoulder. She reached for his belt.

Hawthorne froze the image. He had seen enough.

‘So you were right,’ Torode said. ‘Derek Abbott was blackmailing them.’

‘No,’ Hawthorne said. ‘I was wrong.’

‘What are you talking about? You were the one who found the text that Helen le Mesurier sent Colin Matheson. OMG, Colin . . . What has he got? And Matheson told us—’

‘Matheson was wrong too.’

‘Well, if he wasn’t blackmailing them, what do you think he was doing? Revenge porn? Putting this out on the internet just to annoy them?’

‘It wasn’t Abbott,’ Hawthorne said.

‘Then how did this camera end up in his desk?’

Hawthorne put the camera back where he had found it. Slowly, he explained. ‘Helen le Mesurier wasn’t being blackmailed. She was part of it. And Derek Abbott wasn’t the blackmailer.’