She stood in the doorway. ‘So you don’t believe me.’

I gestured to her to turn around, so I could finish putting my bra on. ‘I do believe you. But that’s the deal. You want something from me, I need to know a bit more about you first.’

Just as I pulled my T-shirt over my head, she turned back again. ‘Suit yourself. I need to pick up some more clothes anyway.’

‘Why? Where have you been staying?’

She walked away from me, as if she hadn’t heard, sniffing her armpit. ‘Can I use your shower? I absolutely reek.’

An hour later, we drove to St John’s Wood. I was exhausted, both by the night’s events and the strange energy Lily gave off beside me. She fidgeted constantly, smoked endless cigarettes, then sat in a silence so loaded I could almost feel the weight of her thoughts.

‘So who was he? That guy last night?’ I kept my face to the front, my voice neutral.

‘Just someone.’

‘You told me he was your boyfriend.’

‘Then that’s who he was.’ Her voice had hardened, her face closed. As we drew nearer to her parents’ house, she crossed her arms in front of her, bringing her knees up to her chin, her gaze set and defiant, as if already in silent battle. I had wondered if she had been telling me the truth about St John’s Wood, but she gestured to a wide, tree-lined street, and told me to take the third left, and we were in the kind of road where diplomats or expat American bankers live, the kind of road that nobody ever seems to go in or come out of. I pulled the car up, gazing out of the window at the tall white stucco buildings, the carefully trimmed yew hedging, and immaculate window boxes.

‘You live here?’

She slammed the passenger door behind her so hard that my little car rattled. ‘I don’t live here. They live here.’

She let herself in and I followed awkwardly, feeling like an intruder. We were in a spacious, high-ceilinged hallway, with parquet flooring and a huge gilt mirror on the wall, a slew of white-card invitations jostling for space in its frame. A vase of beautifully arranged flowers sat on a small antique table. The air was scented with their perfume.

From upstairs came the sound of commotion, possibly children’s voices – it was hard to tell.

‘My half-brothers,’ Lily said dismissively, and walked through to the kitchen, apparently expecting me to follow. It was enormous, in modernist grey, with an endless mushroom-coloured polished-concrete worktop. Everything in it screamed money, from the Dualit toaster to the coffee-maker, which was large and complicated enough not to be out of place in a Milanese café. Lily opened the fridge and scanned it, finally pulling out a box of fresh pineapple pieces that she started to eat with her fingers.

‘Lily?’

A voice from upstairs, urgent, female.

‘Lily, is that you?’ The sound of footsteps racing down.

Lily rolled her eyes.

A blonde woman appeared in the doorway. She stared at me, then at Lily, who was dropping a piece of pineapple languidly into her mouth. She walked over and snatched the container from her hands. ‘Where the hell have you been? The school is beside themselves. Daddy was out driving round the neighbourhood. We thought you’d been murdered! Where were you?’

‘He’s not my dad.’

‘Don’t get smart with me, young lady. You can’t just walk back in here like nothing’s happened! Do you have any idea of the trouble you’ve caused? I was up with your brother half the night, and then I couldn’t sleep for worrying about what had happened to you. I’ve had to cancel our trip to Granny Houghton’s because we didn’t know where you were.’

Lily stared at her coolly. ‘I don’t know why you bothered. You don’t usually care where I am.’

The woman stiffened with rage. She was thin, the kind of thin that comes with faddy diets or compulsive exercise; her hair was expensively cut and coloured so that it looked neither, and she was wearing what I assumed were designer jeans. But her face, tanned as it was, betrayed her: she looked exhausted.

She spun round to me. ‘Is it you she’s been staying with?’

‘Well, yes, but –’

She looked me up and down, and apparently decided she was not enamoured of what she saw. ‘Do you know the trouble you’re causing? Do you have any idea how old she is? What the hell do you want with a girl that young anyway? You must be, what, thirty?’

‘Actually, I –’

‘Is this what it’s about?’ she asked her daughter. ‘Are you having a relationship with this woman?’

‘Oh, Mum, shut up.’ Lily had picked up the pineapple again, and was fishing around in it with her forefinger. ‘It’s not what you think. She hasn’t caused any of it.’ She lowered the last piece of pineapple into her mouth, pausing to chew, perhaps for dramatic effect, before she spoke again. ‘She’s the woman who used to look after my dad. My real dad.’

Tanya Houghton-Miller sat back in the endless cushions of her cream sofa and stirred her coffee. I perched on the edge of the sofa opposite, gazing at the oversized Diptyque candles and the artfully placed Interiors magazines. I was slightly afraid that if I sat back as she had, my coffee would tip into my lap.

‘How did you meet my daughter?’ she said wearily. Her wedding finger sported two of the biggest diamonds I’d ever seen.