It had seemed for one astounding moment that my mother was coming to my defence. But I should have known better. ‘What do you mean?’ I asked, bilious with what I hoped was only morning sickness.

‘Why don’t you ask your cherished sisters? The ones you so kindly took on a cruise, completely forsaking your poor, lonely mother, who loves a cruise but has no one to go with. Six months, I’d say, the affair lasted. Judging by the messages. Being both self-employed, I’m amazed either of you found the time.’

Amber’s laugh vibrated on a high, metallic note. Harry looked at my sister, sheepishly. And that’s when I knew. My heart scrambled and foundered as the truth hit me, hard as a punch. The pain came, rapid and intense, like opening the blinds on a summer’s day when you have a hangover. The knowledge that my sister had slept with my husband settled on my heart, compressing my chest in a vice grip that would never let go.

A shark can smell one tiny droplet of blood in one hundred litres of water. It then traces its prey by following the electricity that is discharged by a terrified animal. My mother gave a gloating grin, her bleached teeth bared. It was the grin of a Great White going in for the kill.

The rest of us were frozen, speechless, as our offspring splashed on in the pool, oblivious. The shimmering bay sparkled at the edge of my vison. I fought the urge to run down the garden and throw myself into it.

What my mother had revealed was so surreal that I lost the power of speech. I sat, welded to my wrought-iron chair. My mind rejected what I’d so clearly heard. My entire body felt hollowed out by the bright white light of a nuclear blast. I was a shell of my former self. My tongue felt suddenly swollen and unyielding. When some words finally came out, they sounded foreign in my mouth. ‘You had . . . an affair? With Amber?’ I ventriloquised.

Amber’s normally alabaster cheeks blazed red, becoming two expressionist splatters of colour.

‘I can’t believe it,’ Emerald gasped. ‘Miss Goody-Two-Shoes. It seems, Amber, that you have entirely failed to grasp the concept of loyal sisterhood – the very first rule of which is not sleeping with your bloody brother-in-law.’

I turned on Amber, eyes ablaze. ‘But you said you hated being touched?’

‘Just not by your husband, obviously,’ our mother qualified, helpfully. ‘You laid the table today, didn’t you, Amber? Forks on the left, and knives in your sister’s back?’