‘He had a nosebleed when I was there, Tom,’ I say, putting on the kettle. ‘I imagine I had his blood on my hands when I touched something: the bannister, probably, or maybe a doorknob. Something that doesn’t get cleaned regularly. It doesn’t prove I killed him. Let them search our house. They’re not going to find anything.’

Tom looks troubled. ‘They could build a circumstantial case,’ he says. ‘I mean, you’ve argued with him, you’ve got his blood on your shoes, and now—’

‘Stacey will confirm where the blood came from,’ I say. ‘And they don’t have a body, Tom. As you pointed out, they still can’t even prove a crime has been committed, much less that I’m responsible. Stop worrying. If I’d murdered him, d’you really think I’d have been this careless?’

Tom’s face clears a little. He’s willing to believe me guilty of killing Felix, but not that I’d be stupid enough to get caught. I love his warped loyalty.

I’m a cardiothoracic surgeon: nerves of steel are part of the job description. But even I am unsettled the police are back so soon, though I’m not going to tell Tom that, of course. It’s not easy, but murder convictions have been secured without a body on nothing more than the accumulation of circumstantial evidence: suspicious bloodstains, the GPS location of a phone, a car that’s been too-thoroughly cleaned. The police don’t need a smoking gun. They just need enough to convince a jury that if it looks like a duck, sounds like a duck, walks like a duck …

I’m lucky Stacey will back me up. Even I can see bloody fingerprints require a little explanation.

‘The kids are upstairs,’ Tom says. ‘What do we tell them?’

‘Peter already knows.’

‘Of course he does,’ Tom says tightly.

‘We tell them the truth, Tom: Felix Porter has disappeared, and the police are looking into it. I told you, they’re not going to find anything because there’s nothing to find.’

Several uniformed officers are fanning out throughout the house. DS Mehdi follows two of them upstairs, and I hear footsteps overhead as they begin their search of the bedrooms. DCI Hollander joins us in the kitchen, his not-quite-handsome, not-quite-interesting face as expressionless as ever.

I pour my tea. ‘Sure I can’t offer you one?’ I ask.

‘Is my wife being arrested?’ Tom demands.

‘We’d like to interview Mrs Downton at the station. As I’ve said, her attendance is voluntary at this stage, and she will be free to leave the police station at any time. However, should she decline to answer our questions on a voluntary basis, we may have no choice but to interview her under caution or arrest her.’