‘Very good,’ said Lea. ‘I do like a young man who has his wits about him.’ The River Lea rises in the Chilterns north-west of London, and skirts the top of the city before making a sharp right-hand turn down the Lea Valley to the Thames. It’s the least urbanised of London’s rivers and the largest, so of course it survived the great stink. Lea must have been one of Oxley’s generation of genii locorum, if not older.

I pulled a face at the child, who looked to be a girl of nursery age, and she pulled a face back. ‘Who’s this?’ I asked.

‘This is Brent,’ said Lea. ‘She’s the youngest.’

‘Hello Brent,’ I said. She was lighter-skinned than her sisters, with brown eyes that might have been called hazel by a good-natured liar, but the belligerent set of her face was unmistakable. She was wearing a miniature red England away strip, predictably the number 11 shirt.

‘You smell funny,’ said Brent.

‘That’s because he’s a wizard,’ Lea told her.

Brent squirmed out of Lea’s grip and grabbed my hand. ‘Come with me,’ she said and tried to drag me through the door. She was surprisingly strong, and I had to brace a little to stay still. ‘I have to bring my crate,’ I told her.

‘Don’t worry, I’ll take care of that,’ said Lea.

I let Brent pull me down the long cool corridor to Mama Thames’s flat. Behind me I heard Lea calling for Uncle Bailiff, and if he would be a dear, could he take the crate to Mama’s flat.

According to Dr Polidari, genii locorum ‘behave as if the imperatives of ceremony are to them as necessary as meat and drink is to man’, and furthermore claimed that they ‘anticipate such events with miraculous facility so that they are always appropriately attired, and if surprised or somehow prevented, show signs of great distress’. Given that he was writing in the late eighteenth century, I like to cut him some slack.