There was a splash, and Beverley came running onto the wharf as if there was a set of stairs hidden under the water. She was as dark and sleekly naked as a seal, and you could have fired a shotgun past my ear and I still wouldn’t have looked away. She turned back to the river and jumped up and down like a kid.

‘I beat you,’ she said.

Oxley came out of the river with as much dignity as a naked, middle-aged white man could be expected to have. ‘Beginner’s luck,’ he said.

Beverley threw herself into the chair next to mine. Her eyes were bright and water was pearling on her arms and on the smooth skin of her shoulders and the slopes of her breasts. She smiled at me, and I tried to keep my eyes on her face. Oxley padded over and sat down opposite and, without preamble and ignoring a look from Isis, grabbed himself a piece of Madeira.

‘Did you enjoy your swim?’ I asked.

‘There are things down there you wouldn’t believe, Peter,’ she said.

‘Your hair’s wet,’ I said.

Beverley touched her straightened hair, which was beginning to frizz. I kept watching as she suddenly remembered she was stark naked. ‘Oh shit,’ she said, and gave Isis a panicked look. ‘Sorry,’ she said.

‘Towels are in the bathroom, dear,’ said Isis.

‘Laters,’ said Beverley, and ran for the back door.

Oxley laughed and reached for another slice of cake. Isis slapped his hand. ‘Go and put some clothes on,’ she said. ‘You appalling old man.’ Oxley sighed and went into the bungalow, Isis watching him fondly as he went.

‘They’re always like that after a swim,’ she said.

‘Do you go swimming too?’ I asked.

‘Oh yes,’ said Isis, and blushed ever so slightly. ‘But I’m still a creature of the riverbank. There’s a balance in them between the water and the land; the more time they spend with us, the more like us they become.’

‘And the more time you spend with them?’

‘Don’t be in a hurry to go into the water,’ said Isis. ‘It’s not a decision you want to rush into.’

Beverley was quiet all the way back up West. I asked her whether she wanted to be dropped off somewhere.

‘Can you take me home?’ she asked. ‘I think I need to talk to my mum.’