The witness can’t be a beneficiary of the patient’s will, so the matter required careful thought. Ivy’s old bridge partner, Thuy, was Chanel’s initial choice. She reminded me that Thuy had been keen to get rid of her husband, which struck us as promising. But we discovered that Thuy’s husband had died at last, leaving Thuy free to move to Tasmania. Then I suggested Ivy’s chiropodist, Kostya. Chanel wondered if we could count on him. He’s young, and the young are generally in favour of the Amendment, but there are always exceptions. Kostya has rimless silver glasses and a bowl cut. Chanel suspected him of holding outdated opinions. Ivy calls him ‘a lovely boy’. Fanta calls him ‘devil’. She’s jealous, of course – jealous of Kostya’s shining nail clippers and safety-slide callus shaver, jealous of Ivy’s swollen feet cradled in his latex-gloved hands. Ivy has antennae for emotional turmoil and exploits it for her own amusement. I’ve seen her show Fanta a greasy playing card and claim that it always turns up when Kostya is due: the jack of hearts, a fair-haired man, a young admirer.

No, there was only ever one realistic choice. Over time, we’ve learned quite a bit about Fanta. Her dishevelled brain informs her that if only she hadn’t been away from her village on that fateful day, a magical force field radiating from her ten-year-old body would have averted the air strike. She entertains thoughts of self-harm, so she sees a psychiatrist and swallows the pills that he hands out like sweets. What use are they? They treat troubles of the mind, and Fanta suffers from turbulence of the soul. It expresses itself in random tremblings, lightning headaches, gastric frenzies, accidental vomits. On the whole, we felt it safe to assume that Fanta would sympathise with anyone who wished to bring their life to a dignified, effortless close. ‘The other advantage,’ said Chanel, ‘is that she probably won’t understand what she’s signing. Anyway, we can put a sheet of paper across the rest of the page, like they do with wills.’

We chose a brownish Sunday afternoon of totally acceptable smoke levels. Ivy and Fanta were promenading up and down Spumante Court in their N95 masks. Chanel had made a red velvet cake. While it cooled on a rack, she was walking backwards the length of the hall (it stretches the hip flexors, she tells me).

I’d had an upsetting start to the day. I got out of bed, swinging my legs out from under Spider-Man, and then I saw. It was all over my right foot – in fact, a few white blotches had appeared on my calf as well. When Chanel woke up, I was standing by her bed, pointing at my leg. She was magnificent – she held out her arms. ‘At least we can go back to sharing a bed,’ she said. ‘I’ve missed you.’ Afterwards, she assured me that I’d find the change painless. Her back and shoulders are affected now, and it’s almost covered her thighs. Lying beside Chanel, I thought back to that girl on the train and the speck she’d left on my trouser leg. I asked Chanel if she remembered anyone vomiting on her. ‘Relax,’ she said. ‘Honestly, I don’t think we should be too concerned. If anything I feel more – well, more empowered as it spreads.’