‘You really got nothing from your dad, did you?’ Beverley sat back in her own seat and tossed the towel into the back. ‘Your mum must have been disappointed. I bet she thought you’d have big curls.’

‘It could have been worse,’ I said. ‘I could have been a girl.’

Beverley unconsciously touched her own hair, which was straightened and side-parted into wings that reached to her shoulders. ‘You don’t know the half of it,’ she said. ‘Which is why you ain’t going to get me out into that.’ She nodded at the rainswept streets.

‘If you’re so supposed to be a goddess …’

‘Orisa,’ said Beverley. ‘We’re Orisa. Not spirits, not local geniuses – Orisa.’

‘Why can’t you do something about the weather?’ I asked.

‘For a start,’ she said with exaggerated slowness, ‘you don’t mess with the weather, and second, this is north London and this manor belongs to my older sisters.’

I’d found a seventeenth-century map of the rivers of London. ‘That would be the Fleet and the Tyburn?’ I asked.

‘You can call her Tyburn if you want to spend the rest of the day dangling from a noose,’ said Beverley. ‘If you ever meet her, you better make sure you call her Lady Ty. Not that you ever want to meet her. Not that she ever wants to meet you.’

‘So you don’t get on with them?’ I asked.

‘Fleet is okay,’ she said. ‘But nosy. Ty is just stuck up. She lives in Mayfair and goes to posh people’s parties and knows “people that matter”.’

‘Mum’s favourite?’

‘Only because she fixes stuff with the politicians,’ said Beverley. ‘Has tea on the terrace at the Palace of Westminster. I get to sit in a car with Nightingale’s errand boy.’

‘If I remember, you’re the one who didn’t want to go home,’ I said.

I spotted Lesley’s car pulling up behind us. She flashed her lights and got out. I quickly leaned back to open the passenger door for her. Rain hit me in the face hard enough to make me splutter, and Lesley practically threw herself onto the back seat.

‘I think it’s going to flood,’ she said and seized my towel, using it to dry her face and hair. She jerked her head at Beverley. ‘Who’s this?’ she asked.

‘Beverley, this is PC Lesley May.’ I turned to Lesley. ‘This is Beverley Brook, river spirit and winner of the London Regional All-comers Continuous Talking Championship five years running.’ Beverley punched me in the arm. Lesley gave her an encouraging smile. ‘Her mother is the Thames, you know.’

‘Really,’ said Lesley. ‘Who’s your dad, then?’

‘That’s complicated,’ said Beverley. ‘Mum said she found me floating down the brook by the Kingston Vale dual carriageway.’

‘In a basket?’ asked Lesley.

‘No, just floating,’ said Beverley.