Hawthorne was less discreet. ‘Haven’t you got it in your head yet, mate? Torode hasn’t got a clue and if he did have one, he wouldn’t know what to do with it. You heard what he said! He’s not going to solve this case. He’s got more chance of finding the meat in his shepherd’s pie than he has of working out who killed le Mesurier. And it probably matters more to him too.’

Terry laughed at that. I was right. He was listening to every word.

Judith and Colin Matheson lived with their three children in a converted barn whose true glory should have been the gardens that surrounded it – and in particular an immaculate lawn that sloped gently down from the edge of the building to the road. But as we drew in, we saw that the lawn had been desecrated. Someone had recently taken a spade to it and gouged out six letters, each one about two metres in length, the fresh earth spelling out a familiar message:

BAN NAB

The work had been done quickly, perhaps under the cover of darkness. The first N was twisted on its side and the final B was too big. It was a particularly ugly piece of vandalism, given how much care had been put into the rest of the garden. Hawthorne and I both saw it as we walked up to the front door but neither of us said anything, as if it would be somehow indecent to comment.

Colin Matheson had seen us arrive and opened the door before we rang the bell. He looked utterly worn out. The first time I’d seen him, he’d reminded me of a junior doctor. Now he was more like an undertaker. ‘I wondered if I might see you today,’ he said – to Hawthorne, not to me. ‘Is it true what I’m hearing about Helen?’

‘She’s disappeared. Yes.’

‘They haven’t found her yet?’

‘They’re looking.’

‘Please come in.’ But Hawthorne stood where he was, examining the garden. He didn’t need to ask anything. Matheson volunteered. ‘It’s horrible, isn’t it? Someone did this on Saturday morning while Judith was out with Lucy, our youngest. She has horse-riding lessons every weekend and our other two are at boarding school, so I expect they knew that the house would be empty. When she got back, this is what she found. I was actually with you when she rang.’

So this explained why Judith Matheson hadn’t come to hear me and Hawthorne give our talk. I had some issues at home. That was what she had said, and Matheson had been deliberately vague about it too.