I nod again. If she wonders why I’m jamming myself in this cubicle door, unmoving, then she doesn’t reveal it.

This woman has no idea who I am. She has no idea that my sister, right behind me, has been sleeping with her husband for five years. That I know intimate details of her life while she knows nothing of mine. We are, as far as she’s concerned, strangers passing pleasantries.

Jude’s wife studies herself in the mirror. She’s a slender, stunningly attractive woman. Not the limp loser or the clingy control freak Lauren has described to me. Tonight she’s wearing a lemon strappy top and a colourful beaded sarong with delicate jewelled flip-flops on her pedicured toes. It is just the most perfect outfit. She runs a lipstick over her full, sensuous lips.

‘Do you need to use the bathroom while we’re here, darling?’

Daisy shakes her head.

‘We’d better get back then or Daddy will be wondering where we’ve got to.’

‘I’m having such a lovely time at this party,’ Daisy declares.

‘Me too,’ Georgia says. ‘Daddy thought you would like it.’

Daisy sighs contentedly and then announces, ‘I have the best daddy in the world.’

Georgia chucks her daughter under the chin. ‘Yes, you do,’ she agrees.

My sister’s lover’s wife smiles in my direction again. She looks like a happy woman, a woman in love, a woman who would never suspect that her husband was cheating on her. Looks, so they say, can be deceptive. But I’d bet a pound on that being wrong in this case.

Georgia gives me a friendly wave. ‘See you later,’ she says.

Another mute wave from me. Then, as the door closes, I sag against the doorpost with relief.

‘It was her, wasn’t it?’ Lauren asks as if she needs my confirmation. ‘They’re so happy together, aren’t they?’

I can’t deny that’s how it seems.

‘She’s wonderful. Did you see her?’

I did.

‘How can I compete with that?’ she says sadly. ‘How can I even want to?’

‘Oh, Lauren.’

‘He’s never going to leave her, is he?’

Do I tell the truth here or do I encourage my sister in her misplaced fantasy of life with her married lover? I opt for the truth. ‘I don’t think so, honey.’

Lauren lets out a keening wail. ‘Why did I have to be dressed as a pineapple?’

Would any other fruit have been better?

‘A bad hair day I might have been able to cope with. But a pineapple? Why couldn’t I have been wearing some chi-chi designer outfit like she was?’

‘It’s no good thinking like that, Lauren.’ I need to try to cheer my sister up before she descends into the gloom of depression. ‘That way madness lies.’