‘Expulsion?’ Tilly was dubious. She was still trying our last diet, which involved eating 90 per cent fermented foods. All she ate was sauerkraut and tempeh, kimchi and pickles. She drank litres of kombucha. A monstrous scoby floated in a jar in our fridge, slick and floppy and yellow like a layer of fat. I had abandoned the fermented diet when I realised how bad I smelled: perpetually gassy, like a compost heap.

‘We’re turning into mummies,’ I’d said.

‘But don’t you feel better?’

I took my belly in both hands, squeezed it.

‘Not yet,’ I said. ‘Do you?’

‘I’ve lost three kilos.’

The Expulsion Cure, explained Dr Bellavit in her introduction, was based on one simple idea: we are all poisoning ourselves. Modern life, with its nanoparticles and parabens, its additives and expedients, is killing us. We ingest things that the human body cannot process. We hold onto them and it makes us sick. And the digestive system is particularly susceptible to such attacks.

‘So what does she mean by expulsion?’ Tilly asked, curled on the couch with a hot water bottle. She sipped her kombucha. ‘Is it like getting expelled from school?’

‘Same principle.’ I was drinking a tisane made from stinging nettles. It was bitter, but I liked to think of it scrubbing my insides like drain cleaner, removing the scaly deposits, leaving things shiny. ‘You identify the undesirables and you throw them out.’

‘Where do they go?’ she asked.

‘They vanish,’ I said.

After the flight, we hired a driver to take us out of town to the ferry terminal. As far as we knew, there were no other residents on the island besides those at Dr Bellavit’s retreat. The ferry’s windows were filmed with grease, and there were seams of grime worked into the cracks in the plastic seats.

As we boarded, the ferry driver said, ‘Staying with Dr Bellavit?’

‘Of course,’ I said.

The man spat into the water. He seemed fascinated by the small foamy spot of it floating away.

‘It’s just – you don’t look sick.’

He raised his gaze back to us. His neck and chest were a deep, uniform pink-red. I was aware of how the heat made my clothes cling, of the salt in my mouth from where I’d licked sweat from my top lip.

‘We are sick,’ Tilly said.

The driver raised his hands as if in surrender.

He wasn’t the first person to suggest we weren’t really sick. We’d had doctors tell us as much. I was once asked by a psychiatrist if I understood the concept of secondary gain. I nodded enough to get prescriptions for Xanax and Zoloft, listening to the mucus in his nostrils – he was perpetually sniffing – vibrate as he talked.