‘Oh, more. Much more. Plus she had all this money in her bank account that she refused to spend because she was supposedly saving it for a rainy day. She was in her eighties! It was already pissing down.’ Fiona chuckled. ‘Maisie saw the opportunity immediately. Dinah was exactly the kind of person we’d been looking for. Loaded and clueless and lonely. Most importantly, she had no immediate family. There was a sister who was in a nursing home. A niece and her offspring. But that was it.’

Fiona was enjoying this. The only other person she’d told this story to was Lucy, huddled together in Lucy’s cell – sorry,room. ‘Maisie told Dinah she had a friend who was looking for somewhere to stay, then took me round to meet her. I thickened my accent, which she loved because she’d spent some time in Australiawhen she was young. She talked at length about the wonderful vineyards in Margaret River.Myfamily used to buy cheap crap from the bottle-o. We came to an agreement. She would provide me with lodgings, and in return I’d keep the place clean and do some gardening.’

Rose was beginning to fidget, so Fiona hurried up.

‘The point was, I wanted Dinah to change her will so when she died everything went to me. Early on, she’d told me she was going to leave her estate to her niece, Verity, and her children. Verity would pop round every now and then, have a nose round, examine the valuables, check the house wasn’t going to fall down. I could see the pound signs in her eyes, even though she was already well-off and would never want for anything. One day I found her taking photos of the paintings on the wall. Dinah also had this sketch that Warhol had given her, which Verity was always asking to look at. She asked if she could take it to get it valued, but Dinah wouldn’t let her remove it from the house.

‘I had three objectives: One, let Dinah know that Verity was a gold digger and drive a wedge between them. Two, take Verity’s place in the will. And three, because Dinah was in annoyingly good health and could easily have lived to a hundred, help her get on with shuffling off this mortal coil.’

‘This mortal what?’

‘Coil. I needed to help her cark it.’

Rose still looked confused.

‘Die.’

‘Ah. Got it.’

Fiona smiled. ‘The first and second parts were relatively easy. Dinah already knew Verity only loved her for her money, and she accurately thought the great-nieces were a pair of spoiled brats. I kept telling Dinah that if I were her, I would leave my money to charity. A cats’ home, or something in her daughter’s name: a drugrehab centre, maybe. I knew she’d hate that idea because she didn’t want her family name forever associated with heroin. She didn’t like cats either. But it was all designed to make her think about changing her will.

‘I used all my charm’ – everything she had learned about normal human behaviour – ‘to win her over. I would hide her favourite pieces of jewellery or her purse so she thought she’d lost them, then miraculously find them, showing how honest I was and how she couldn’t live without me. I pretended to be devoutly religious and went to church with her every Sunday. I cut her hair for her and did revolting things like massaging her bunions.’ She shuddered at the memory. ‘Finally, I saved her life.’

Rose, who had appeared to be drifting into a daydream, suddenly paid attention. ‘How?’

‘I knocked over a candle that Dinah had lit downstairs. She had actually snuffed it out before going to bed, but I relit it and used it to start a small fire. Then I rushed into her room and told her we needed to get out. It was a gamble. If the fire had spread and destroyed the house, I’d have had nowhere to live, not to mention the effect on the inheritance I was banking on. But I called 999 almost as soon as I lit the candle, so they arrived quickly and put it out before too much damage was done. Dinah was, as you can imagine, supremely grateful. Also, Maisie phoned, pretending to be Verity, calling not to check on her aunt but to ensure the Warhol sketch and all the other valuable possessions were okay.’ Fiona laughed at the memory. Maisie had been so deliciously devious. ‘Shortly after that, Dinah changed her will to leave everything to yours truly.’

‘Wow.’

‘Yep. And that meant it was time for the third part of the plan.’

‘Pushing her off this mortal coil.’

‘Exactly. Which is where Maisie really came in. She’d done this before, you see. She knew all about poisons. Drugs. Things you could slip into someone’s food or drink, to slowly poison them over an extended period. Thallium, mostly. I was cooking Dinah’s dinner every day, so it was easy to add it to her food. Tiny amounts that only had a big effect over time. We wanted it to look like she’d died of natural causes. And it would have worked, if it wasn’t for Patrick.’

Rose had become far more attentive once Fiona had started talking about poison. ‘That’s why you wanted revenge on him?’

‘Yep. He was an old friend of Dinah’s late husband, the Tory MP. Often quoted him in stories about the soaring crime rate. He popped round unannounced one afternoon, because he was visiting a friend in the area. At this point, Dinah was in a bad way. Her hair was thinning, she was delirious half the time, and she had awful stomach pains. She was so delirious that she didn’t notice that the doctor who kept visiting her was actually Maisie in a white coat.’

She sighed. ‘I wasn’t there when Patrick came round. I’d popped out to do some shopping. Dinah let him in, apparently convinced he was some lover she’d had in the sixties, and tried to slobber all over him. When he saw the state she was in, he rushed her to the hospital. He’d seen thallium poisoning before, reported on a case of it, so he was sure he knew what it was. They treated her and she made a full recovery. Told all about her lodger.’

‘And that’s when you went to prison?’

‘Yes. Well, after a while. There was an investigation. Interviews. Evidence had to be gathered. It took a while. And then, one morning, the police turned up. We tried to get away but were arrested.’ She glowered at the memory of it, then hurried through the rest of the story.

‘We hired Max as our lawyer. He told us the police’s evidence was overwhelming. The niece, Verity, was ready to testify, as wasDinah herself. Max advised us to plead guilty. The arsehole. Then he brought me a letter from Maisie. We weren’t allowed to see each other, you see.’

Rose was leaning forward now, gripped. ‘What did the letter say?’

‘She told me to read it, then destroy it. The letter said that she wished me luck. That she had written another letter confessing to the poisoning, saying I wasn’t involved at all and hadn’t known about it. And at the end she said that she had decided she couldn’t face prison, even for a few years.I was born to be free, she wrote.I can never be caged.’

Rose’s mouth hung open. ‘What did she mean?’

Fiona didn’t really feel emotions towards other people. Concern, pity, love: they were alien to her. But this was the closest she had ever come to feeling upset about something that had happened to someone else. Perhaps it was self-pity – the sensation that she’d been abandoned, left alone. But she had yelled at Max, told him to call the prison where they were holding Maisie. While he did that, she ripped the letter up into tiny pieces, chewing and swallowing it.

Max had returned just as she forced down the final shred, his face ashen, to tell her that Maisie had provoked the hardest, most violent criminal in the prison into a fight. The woman and her cronies had beaten Maisie to a pulp. She was in a coma.

Two days later, she died.