‘Because it’s my job – that’s what the Folly is about.’

‘No,’ said Beverley. ‘That’s what you’ve decided the Folly is about. I wonder if the Nightingale thinks the same as you do.’

‘I don’t know,’ I said. ‘But that’s not the point.’

‘Really?’ asked Beverley. ‘You can’t let this case go – not even for a quiet life?’

There was a long pause while Beverley looked me right in the eye and I was suddenly worried that she was going to ask me to cease and desist as a personal favour to her. And if she did, I wasn’t sure what I was going to say. But then she shook her head and waved her burger at me.

‘Alright, I’ll do it. But it’s going to cost you,’ she said.

‘What is it this time?’

‘Maksim’s putting in some baffles where I run across the common,’ she said. Maksim was the administrator and sole employee of the Beverley Brook Conservation Improvement Trust. He was also a terrifying former Russian mobster who’d come into Beverley’s ‘service’ via a complicated and morally ambiguous route. ‘He needs a hand.’

‘Fine,’ I said. ‘As long as you come and watch.’

Beverley grinned. ‘You know I like it when you do improvements,’ she said.

I know she liked to get me in the water with my clothes on – I blame Colin Firth for that.

I had a sudden brainwave while driving back west, so when I got to Belgravia I hunted down Guleed, who was typing up that morning’s statements from St Paul’s school for girls with rich parents. I showed her the picture I’d taken of the collage on Olivia’s wall, with the young curly haired woman who had cropped up so frequently.

‘Spot this one?’ I asked.

‘Oh yes,’ said Guleed and checked her notebook. ‘Phoebe Beaumont-Jones – shared a couple of classes with your Olivia.’

I thought of the picture of them standing together in France, arms comfortably around each other’s waists.

‘Not best friends?’ I asked.

‘Nobody said anything,’ said Guleed. ‘Least of all Phoebe herself.’

‘They definitely look like friends in the picture,’ I said.

‘Do you think she was at the party?’ asked Guleed.

None of the witnesses had identified her, but if she was Olivia’s friend rather than theirs they might have overlooked her. Or were they scared of Olivia, or of Phoebe Beaumont-Jones?

You can’t go by appearances – I once helped put away a gang of steamers who’d been working Oxford Street at the behest of an OAP with a dodgy hip and pipe cleaner arms. They were so terrified of him that not one of the gang would grass him up. I asked one of them why – off the record – and he told me that the geezer had no off switch, and once he started in that was it. You were dead meat.