“I’m not sure,” I said honestly. “At first I thought you were trying to coerce her into reassigning the power of attorney…but now I think it was straightforward cruelty. You punished her because she wasn’t mentally competent to do what you wanted…and then found you enjoyed it. Simple as that. It’s why most sadists do what they do.”

She stood up abruptly. “I don’t have to listen to this.”

“I suggest you do,” I said mildly, “otherwise you’ll be hearing it from Inspector Bagley. So far I’ve told him very little, but only because your mother didn’t die. If she had, we wouldn’t be having this conversation…you’d be at the police station answering questions about murder. You’ll just answer different ones if you walk out now.”

“No one’s going to believe you.”

“I wouldn’t rely on that. It just needs a chink of doubt.” I tossed my still-smoking butt into the sink. “Your problem’s the Aga. The Burton’s delivery notes prove it was off for two months. But if Jess had been responsible for that she’d have relit it…because she’s the only one who knows how.”

Madeleine shook with suppressed anger. “I suppose she put you up to this. She’s always hated me…always told lies about me.”

“Is that right? I thought lies were your specialty.” I ticked my fingers. “Predatory lesbian…stalker…obsessive…mentally ill…servant mentality…tenant farmer…syphilitic grandmother…hates men…only has sex with dogs. What have I left out? Oh, yes. Your grandfather had a yen for maids and raped every poor girl who entered his service, including Jess’s grandmother.”

She looked shell-shocked. “I’ll sue you for slander if you repeat that.”

“The bit about the rape? Is that not true? I thought he handed over fifteen hundred acres in compensation after his son was born? It was cheap at the price…the land cost him nothing and his reputation would have been in ruins if Jess’s grandmother had gone to the police.”

“It’s all lies,” she hissed. “There was no saying who the father was. Mrs. Derbyshire was a tramp…she slept with anyone and everyone.”

I shrugged. “It’s easily proved by a DNA test. The closest match will be Jess and your mother.”

“I won’t allow it.”

“It’s not your permission to give. Lily handed that right to her solicitor.” I smiled at her. “It’ll make a grand story. Skeletons rattle in Wright closet as DNA proves link. Abuse jumps a generation as failed artist’s wife seeks to silence mother. Career scrounger cites class as justification for sadism…”

Jess had predicted she’d take a swipe at me if I provoked her enough-“Lily was afraid of Madeleine, and her kid’s completely terrified”-so I should have been expecting it. But she still managed to take me by surprise. I’ve come to the conclusion that I’m really quite naïve about the levels of violence that some people are prepared to use. I shouldn’t be-I’ve seen too much of it in Africa and the Middle East-but my experience of war is different. I’ve always been a bystander, and never a participant.

MacKenzie should have taught me the dangers of complacency. And he did, as far as he was concerned. But it never occurred to me that a twisted psychopath, who raped and mutilated women, had anything in common with a Dresden china blonde in high heels and an elegant shirtwaist. I should have paid more attention to Jess. From day one, she had described Madeleine as a manipulative, narcissistic personality of shallow emotions, who demanded instant gratification, resorted to bullying when she didn’t get it and showed no remorse for the impact her behaviour had on others.

And that’s as good a definition of a psychopath as you’ll find.

I’D EXPECTED a slap across the face, not an all-out assault on my eyes with crimson fingernails. I was on the floor, shielding my head from her kicking shoes, almost before I knew she’d attacked me. It was very fast and very noisy. I remember her screaming “Bitch” as she grabbed me by the hair and spun me round so that she could aim at my face, but I curled into a tight ball and took most of the punishment on my arms and back.

She wasn’t fit enough to keep it up for long. The kicks became less frequent as her mouth took over. How dare I question her? Didn’t I know who she was? Who did I think I was? It was an interesting insight into her character. At no point did she consider the consequences of what she was doing or whether my provocation had been deliberate. Quite simply, a red mist descended and she went ape.

I won’t pretend it wasn’t painful-her shoes were leather with pointed toes-but it was a walk in the park compared with Baghdad. Her balance was precarious, her aim was bad, and her foot had very little weight behind it. I put up with it because anger, like alcohol, loosens tongues, and she thought my refusal to fight back meant she had nothing to fear.

“It was the best day of my life when the Derbyshires died…the only one left was the runt…and she was so feeble she tried to kill herself. I told my mother she should have let her bleed to death…and do you know what she said? Be nice… you owe it to her…you have Nathaniel. God, I hated her! She couldn’t keep her mouth shut…had to talk to her brother…had to apologize…wanted me to call him uncle. I said I’d rather die than admit I was related to a slut’s bastard…and he laughed and said the feeling was mutual. Then he had the nerve to beg my mother to keep the secret…for the sake of his children…”

She referred obliquely to the cruelty she and Nathaniel had inflicted on Lily. “I told Nathaniel no one would help her…she was such a bitch they never went near her. Even Peter wasn’t that bothered…he said the troll would always tell him if things got worse. Blame her for neglect…she’s the one who walked away and left me to deal with it…as if I were the servant…”

I’d have let her run her head even farther into the noose if she hadn’t decided to grind her heel into my hip bone. Enough was enough. I was out from under her heel and on my feet while her gabby mouth was still flapping about her status in life, and she wasn’t ready for the pile-driving charge that drove her against the Aga rail and knocked the wind out of her.

I don’t think she noticed when I slipped her right wrist through a fabric loop and pulled it tight, but she certainly struggled as I grabbed her left wrist and yanked it the other way. “My God, you really are a piece of work,” I said in disgust before raising my eyes to the webcam on a cupboard next to the sink. “Did you get all that, Jess?”

Jess pushed the scullery door wide and the sound of her hard-drive fan intruded noticeably into the kitchen. “The camera in the hall failed,” she said, coming in, “but the three in here worked perfectly. Are you OK? It looked pretty bad on screen but as you didn’t yell-” she broke off to stare at Madeleine. “I don’t think she’s ever taken on anyone of her own size before…just frail old ladies and children.”

I rubbed my shoulder gingerly where a bruise was beginning to form. “Not so different from MacKenzie then. I wonder what else they have in common.”

“Arrogance,” said Jess, examining the other woman curiously as if she’d never seen her before. “I should have guessed it was Dad who wanted it kept secret. He used to say if any of us pretended we were better than we were, he’d disown us. I thought it was because we came from working stock, but now-” she jerked her chin at Madeleine-“I think he was terrified we’d turn into this.”

MADELEINE’S IGNORANCE of Jess’s proficiency in computer technology and film-making meant we could only convince her of what we had by moving Jess’s hard-drive and monitor into the kitchen, playing the scene again from the perspective of three different cameras and demonstrating how easy it was to copy the images to disk. She harangued us fluently throughout, accusing us of blackmail and kidnap-both of which were true-but when I retrieved a pack of envelopes from the office and started addressing them to the inhabitants of Winterbourne Barton, she quieted down.