“Then we’re back to square one,” he said, “unless your boy Jack is cleverer than you think. What if he really did kill the duke but made it so obvious and blundering that we’d come to the conclusion he couldn’t possibly have done it?”

“That’s possible too, I suppose,” I had to admit. “But I’m sure that coat is important. Why would Jack cover the body with a coat? Why would anyone? If the murderer wanted to hide the body, he could have dragged it into the nearest bushes. It was just as obvious with a coat over it.”

“Unless he wasn’t strong enough to move the body,” the inspector said. “Or she wasn’t strong enough.”

We stared at each other, digesting this. I remembered that Edwina had said she would do anything to stop Cedric from making Marcel his heir. But surely she would never resort to killing her own son?

“There is one other thing,” I said tentatively. “Remember I mentioned to you that the duke went out early to post a letter. And when I last spoke to you, the letter hadn’t been found.”

“That is correct,” he said.

“Now I think this letter might be important,” I went on. “He insisted on posting it himself, which is unusual in a house like this, where such a task could easily be handled by servants. Maybe it was important enough that someone killed him to prevent him from posting it.”

“Go on,” he said.

Emboldened by his apparent interest, I began to speak more freely. “Of course it’s possible that he had already gone as far as the postbox and was returning when he met his killer. Might I suggest that you have your men inquire at the post office whether the postman picked up a letter from the duke this morning and to whom it was addressed? I’m sure it would have been noticed because very few letters would find their way to an out-of-the-way postbox in a small lane. And the envelope would have had the Eynsford crest on the back. Postmen notice things like that.”

The chief inspector nodded. “Might be worth following up on. I thank you for your insights, my lady. But my money is still on the Australian boy. If we find a nice, clean set of his prints on the knife handle, over any other prints, then I’m making an arrest. I don’t care if he is a ruddy duke.”

He broke off as one of his constables approached us. “I was asked to tell you that the MO has taken the body, guv. And Phelps has finished with the fingerprinting. I suppose you want to be there when we have a go at the knife? Are we going to take the evidence back to HQ?”