Beverley took my hand and led to me along until she found a place where we could sit down on the edge and dangle our feet, minus shoes obviously, in the water. It was midmorning and the sun had come into its full heat so we stayed in the shade of what Beverley identified as a stand of silver birch but which looked more red-brown to me.

‘You see this river,’ said Beverley. ‘Like I said, lots of potential but nobody’s home. What it needs is something to stir it up – sometimes this can be perfectly natural, and sometimes you can give it a helping hand.’

I thought of Mama Thames, who claimed to have gone into the river as a suicidal nursing student and walked out a goddess. And with a personality like that, was it any wonder that she sparked the process in her tributaries, or that they so took after her?

‘We were making a donation?’ I asked.

‘I know you want to be a father,’ said Beverley, ‘but there were no genes involved whatsoever, no transfer of information, we were strictly catalytic in the process.’

‘You’re sure?’

‘Tell you what,’ she said. ‘If we come back in ten years and he’s watching Doctor Who, you can call me a liar.’

‘He?’

‘I think this is going to be a boy river,’ said Beverley, kicking up spray with her feet. ‘But you never know – it might have its own view on the subject.’

‘You know, I’m pretty certain I’m not supposed to do shit like this,’ I said.

Beverley put an arm around my shoulder and leaned in to talk softly in my ear.

‘How about this then, Peter,’ she said. ‘You’ve been part of something that no wizard has ever been part of before. You know something that’s not in their books.’

I wanted to say that lots of things weren’t in the libraries of the wise, including plate tectonics, molecular biology and the complete works of J.K. Rowling, but she’d probably say that I was missing the point. I must have hesitated long enough for Beverley to think she’d won the argument.

‘You should feel privileged,’ she said. And rested her head on my shoulder.

‘I shall write it up as a paper, as soon as I get home,’ I said.

‘You do that,’ she said. ‘I dare you.’

‘My milkshake brings all the gods to the yard,’ I said.

‘Damn right, it’s better than yours,’ said Beverley. ‘I could teach you but I’d have to charge.’

The next line that came into my head was Flat bottomed barges you make the river world go round! But I decided to keep that one to myself.