I was fighting the urge to fling myself to my knees before her and put my face between her breasts and go blubby, blubby, blubby. When she offered me a seat I was so hard it was painful to sit down.

I caught Beverley snickering behind her hand. So did Mama Thames, who sent the teenager scuttling for the kitchen. This I know for a fact: the reason African women have children is so that there’s someone else to do the housework.

‘Would you like some tea?’ asked Mama Thames.

I declined politely. Nightingale had been very specific: don’t eat or drink anything under her roof. ‘Do that,’ he’d said, ‘and she’ll have her hooks in you.’ My mum would have taken such a refusal as an insult, but Mama Thames just inclined her head graciously. Perhaps this too was all part of the arrangement.

‘Your Master,’ she said. ‘He is well?’

‘Yes ma’am,’ I said.

‘He does seem to get better as he gets older, does our Master Nightingale,’ she said. Before I could ask what she meant, she had asked after my parents. ‘Your mother is a Fula – yes?’ she asked.

‘From Sierra Leone,’ I said.

‘And your father no longer plays, I believe?’

‘You know my father?’

‘No,’ she said, and gave me a knowing smile. ‘Only in the sense that all the musicians of London belong to me, especially the jazz and bluesmen. It’s a river thing.’

‘Are you on speaking terms with the Mississippi, then?’ I asked. My father always swore that jazz, like the blues, was born in the muddy waters of the Mississippi. My mother swore that it came from the bottle, like all the devil’s best work. I’d been taking the piss a little bit, but it suddenly occurred to me that if there was a Mother Thames, why not a god of the Old Man River, and if that was so, did they talk? Did they have long phone calls about silting, watersheds and the need for flood management in the tidal regions? Or did they email or text or twitter?

With that reality check, I realised that some of the glamour was wearing off. I think Mama Thames must have sensed it too, because she gave me a shrewd look and nodded. ‘Yes,’ she said. ‘I see how it is now. How clever of your Master to choose you, and they say you can’t teach an old dog new tricks.’

Two weeks of similarly impenetrable remarks from Nightingale meant that I had developed a sophisticated counter-measure to gnomic utterances – I changed the subject.

‘How did you come to be Goddess of the Thames?’ I asked.