‘Oh, yeah, I remember Princess Luna,’ he said. ‘I thought that had sort of stopped. Nicky used to demand extra sweets for Princess Luna and then scoff the lot herself. Vicky got very uptight about it – all those childhood obesity articles in the women’s section of the Sundays.’

Apparently, there was one of those mother-daughter power struggles – like those that so enliven the lives of my mum’s relatives – which Derek had made a point of staying out of. Finally, Nicole stopped talking about her imaginary friend, and Derek just assumed it had been a phase.

‘Unless it was real,’ he said. ‘And just wandered off one day.’

And how many invisible friends are not imaginary, I asked myself as he walked off to join the search team. What if this stuff is way more common than even the Folly thinks it is? What if it wasn’t just children – what if it was schizophrenics as well?

I carry a notebook with a list of these kinds of questions, and it gets longer every month – especially since Nightingale made answering them conditional on my advancement through the forms and wisdoms.

According to DS Cole, Victoria Lacey and Joanne Marstowe were spending the morning together at the Marstowe house while kind relatives, of which Joanne had almost as many as my mum, were taking the two older boys out for a day in Hereford. When I arrived in the suddenly – and suspiciously – neat and tidy kitchen I found the two mothers seated on either side of the table while DS Cole sat at the end and acted as de facto referee. You could have fried an egg in the space between the two women, and I almost turned on my heel and walked back out again.

‘Peter,’ said Joanne. ‘Would you like some tea?’ She was already up and bustling before I could answer, so I said I would and deliberately took her seat to break up the confrontation.

Victoria stared at me as I sat down, her face a mask. ‘Is it true you’ve been asking about Nicky’s silly imaginary friends?’

I gave her the same flannel I’d given her husband and I think she bought it, or at least was willing to convince herself that the police hadn’t suddenly gone completely bonkers.

‘Who wants tea?’ asked Joanne.

I said yes again, Victoria said no and DS Cole gazed longingly at the kitchen door.

‘You know what it’s like with children,’ said Victoria. ‘Once they get an idea in their head they won’t let go – the more you try to stop them the harder they cling on to it. But you can’t just appease them forever – can you?’

Joanne plonked a mug of tea in front of me and I asked her if Hannah had ever claimed to have met Princess Luna.