Olivier would read through everything I had written and tell me what he liked and what he didn’t. What could be more funny. What could be more emotional. I was impressed with his insight. He had an innate understanding of what was important in writing: to leave the reader feeling something. Yet again I questioned the wisdom of him doing law. It seemed so dry, so driven by facts and rules and laws, so black and white.

‘Maybe it won’t be forever,’ he told me. ‘But I would be letting my family down, if I don’t follow my father.’

I was impressed with his sense of duty, but I felt sad for him that it didn’t speak to his heart. I knew how much he loved books, and reading – his room was piled high with paperbacks. He couldn’t pass the bouquinistes without buying something to add to his collection. But he seemed resigned to his fate, so there was nothing I could do or say.

I didn’t neglect Nathalie in all of this. I’d always disliked girls who dropped their friends when they fell in love. I had plenty of time to see her during the day, when Olivier was at lectures. My usual routine was to tidy the children’s rooms and make their beds, put on a wash, then go into the kitchen to make a shopping list. Then I’d head out to meet Nathalie for a coffee at the café at the end of the street, sitting outside if it was sunny, reading a few pages of Le Grand Meaulnes while I waited for her. It was a slow process, and I needed my mini Collins Gem French Dictionary for more than half the words.

She would bounce up, always late, always full of some crazy story, always looking amazing, wearing things I would never dare to. She relished every detail of my love affair with Olivier, living it vicariously, for she shied away from relationships, blaming her father’s infidelity. She had casual flings, but she didn’t seem to want to get close to anyone.

‘Not all men are like your dad,’ I told her.

‘Yes, but I don’t know how to figure out which ones are and which ones aren’t. So it’s easier not to get involved.’

I found it sad that she was so scarred by her dad’s behaviour, but it was the main reason I didn’t divulge what had happened between me and Jean Louis. She was vituperative about the secretary her dad had run off with, and I didn’t want to be the object of her disapproval. She was terrifying when she was scathing, and anyway, I had berated myself enough.

I did share my worries about Corinne with her, though. I still could never tell what mood she was going to be in.

‘Honey, all Parisian women are difficult. You won’t find one who’s easy to work for.’

‘There’s something more, though,’ I protested. ‘It’s not just that she’s difficult. I think she might be ill.’

‘Maybe she has PND?’

‘PND?’ Nathalie was full of acronyms I didn’t understand.

‘Postnatal depression.’

‘Oh, you mean like baby blues?’ I remembered my mum bandying the words around when my aunt had my youngest cousin and didn’t seem to be coping very well.

Nathalie nodded. ‘It can drive totally normal women nuts. I think my mum had it, after my brother was born. That was when she started drinking. Like, really drinking.’

I could see her getting agitated. She hated talking about her family. As far as Nathalie was concerned, her life had started the day she landed at Charles de Gaulle and Gigi was waiting at the arrivals gate to greet her. So we dropped the subject.

December arrived, and with it the excitement of Christmas around the corner. I was staying in Paris, because it was too expensive to travel, and although it would be strange, being away from home, I was looking forward to it.

Corinne seemed full of festive spirit and began to decorate the apartment. The decorations were opulent: strings of glass baubles and huge bunches of dark red roses and swathes of ivy, and a massive tree that took two men to drag up the stairs.

‘What would the children like for Christmas?’ she asked me one afternoon, her pencil poised over a list.

‘Oh, Charlotte wants roller skates, more than anything,’ I told her. She would gaze at other children skating in the Tuileries, her eyes round with want.

‘Bonne idée!’ Corinne looked delighted with this suggestion and wrote it down. ‘And for Hugo too?’

‘No. Hugo wants a kite.’

‘Un cerf volant!’ She seemed to think I was a genius, and, for a few minutes, we felt quite close, laughing together, almost like sisters.

She was complicated, I decided. She seemed like two different people – or maybe more. There was the scary businesswoman – all spindly heels and dark nails. There was relaxed Corinne: the warm, loving mother and wife and thoughtful boss. And then there was the vulnerable, needy one who would appear out of nowhere, who would descend into a total wreck at the drop of a hat. I hadn’t seen that version for a while and thought maybe she was gone for good. I even thought it might be because of me that she was on the mend. Somehow, I’d forgotten the roller coaster, how her mood would plummet for no reason, out of the blue.

One day, when I got back from shopping, I found her catatonic in the bath, an empty wine glass on the side. She’d left her bathroom door wide open. I rushed in, plunging my hands in the water to pull her out. She was freezing.

‘Have you taken something?’ I asked her, panicking, thinking she might have overdosed on the sleeping pills I knew she took.

Her lips were blue, but she shook her head. I wrapped a big towel around her, then led her into her bedroom.

‘You must get dry, and warm. I’ll make you a hot drink.’

I ran to the kitchen. My hands were shaking as I made her a hot chocolate. There was something really wrong with her. I thought about my conversation with Nathalie. But Arthur was nine months, nearly. Not a newborn. I wondered if she’d been like this before he was born. Should I ask her? Or maybe I should ask Jean Louis, in private.