I’m a bit thrown. Elinor doesn’t usually bring up tricksy family subjects.

‘I know,’ I say shortly.

‘There are elements of Luke’s character I find …’ She pauses again. ‘Hard to comprehend.’

‘Elinor, I really can’t get into this,’ I say uncomfortably. ‘I can’t talk about it. It was between you and Luke. I don’t even know what happened, except that you said something about Annabel—’

Is it my imagination, or does Elinor twitch slightly? Her hands are still shuffling jigsaw pieces but her eyes are distant. ‘Luke was devoted to … that woman,’ she says.

That woman again. Yes, and that’s exactly what he calls you, I feel like saying.

But of course I don’t. I just sip my tea, watching her with more and more curiosity. Who knows what’s going on underneath that lacquered hair. Has she been thinking about her row with Luke all this time? Has she finally realized how she’s wrong-footed herself? Has she finally realized what she’s been missing out on?

I’ve never known such a mystery as Elinor. I’d so love to climb inside her head, just once, and see what makes her tick.

‘I only met her once.’ Elinor raises her head with a questioning expression. ‘She did not seem particularly refined. Or elegant.’

‘Is that what you said to Luke?’ I can’t help exclaiming furiously. ‘That Annabel wasn’t refined or elegant? No wonder he walked out on you. She’s died, Elinor! He’s devastated.’

‘No,’ says Elinor, and now there’s a definite little spasm under her eye. It must be the only square millimetre which isn’t Botoxed. ‘That is not what I said. I am merely trying to understand his overreaction.’

‘Luke never overreacts!’ I retort angrily.

OK, this isn’t quite true. I have to admit Luke has been known to overreact to things on occasion. But honestly. I feel like hitting Elinor over the head with her silver teapot.

‘He loved her,’ she says now – and I can’t tell if it’s a statement or a question.

‘Yes! He loved her!’ I glare at Elinor. ‘Of course he did!’

‘Why?’

I stare at her suspiciously, wondering if she’s trying to score some kind of point – but then I realize she’s serious. She’s actually asking me why.

‘What do you mean, why?’ I snap in frustration. ‘How can you ask why? She was his mother!’

There’s a sharp silence. My words seem to be sitting in the still air. I can feel a prickly, awkward feeling creeping over me.

Because, of course, Annabel wasn’t Luke’s mother. Strictly speaking, Elinor’s his mother. The difference is, Annabel knew how to be a mother.

Elinor has no idea what being a mother is about. If she did, she wouldn’t have abandoned Luke and his father in the first place, when Luke was still tiny. If she did, she wouldn’t have turned away that day he came to New York aged fourteen. I’ll never forget him telling me about the way he waited outside her apartment building, desperate to meet the mythical, glamorous mother he never saw. The way she came out at last, immaculate and beautiful like a queen. He told me that she saw him across the street, that she must have known exactly who he was … but pretended she didn’t. She just got in a taxi and disappeared. And they never saw each other again till he was an adult.

So of course he got a bit obsessed with Elinor. And of course she let him down, again and again. Annabel totally understood it and was endlessly patient and supportive – even when Luke grew up and became in thrall to Elinor. She knew he was dazzled by his natural mother; she knew he’d get hurt by her. All she wanted to do was protect him as much as she could, just like any mother would.

Whereas Elinor … about anything.

Half of me wants to say, ‘You know what, Elinor? Forget it, you’ll never understand.’ But the other half wants to rise to the challenge. I want to try and make her understand, even if it turns out to be impossible. I take a deep breath, trying to organize my thoughts. I feel like I’m about to explain a foreign language to her.

‘Annabel loved Luke,’ I say at last, folding my napkin into pleats. ‘Unconditionally. She loved him for all his good points and all his flaws. And she didn’t want anything in return.’

In all the time I’ve known Luke, Elinor has only been interested in him when he could do something for her or raise money for her stupid charity, or cast her some reflected glory. Even the wedding she put on for us in the Plaza was all about her and her position in society.