‘Peerie Lizzie’s song,’ he said. ‘You know the tune written by Marty Thomson. Have the kids in your school learned it?’

‘I haven’t taught it to them. But then I don’t teach music, and they might have learned it before I arrived at the school.’ She was still sitting on the floor and looked up at him. ‘Why is it important?’

‘It probably isn’t, but that old story of Lizzie seems to weave its way through the inquiry.’ He knew he couldn’t be specific, but still he valued her opinion. ‘You don’t believe in ghosts, do you?’

She laughed. He was glad to see it; he had the sense that she didn’t laugh very often. ‘Not the sort that walk through walls. But maybe I think that sometimes the past comes back to haunt us.’ She paused and he knew better than to speak. He’d learned some tricks from Jimmy Perez. Louisa went on. ‘Last year I was contacted by a social worker. My birth mother was trying to get in touch with me.’

‘Did you meet her?’

‘Once. But she was very needy. Still an addict, after all these years. Thinking that, with my good job and my settled life, I could help her get straight.’

Or fund her habit, Sandy thought.

‘And I only have so much to give, Sandy. I had to make a choice. Between my birth mother and the mother who took me on thirty years ago.’

‘You made the right decision.’ He wished he could tell Louisa how much he admired her, but it was all he could think of to say.

‘I’m sure I did, but it doesn’t stop me thinking about the other woman occasionally.’ She got to her feet. Obviously she’d decided it was time for him to go. ‘This was the easy choice. Running away north to be in my comfort zone. It feels a bit cowardly.’

‘You made the right decision.’ He repeated the words slowly, hoping that she might believe him this time.

‘Is this all you came for, Sandy? To ask me about a children’s song. You could have done that over the phone.’

‘I was glad of the excuse to spend some time with you,’ he said. ‘And pleased to escape from the investigation for a while.’

There was another awkward silence, broken by the sound of Mavis’s gentle snoring. He glanced out to the garden to see if her birds were still feeding on the table, but the mist had come in again and it was hard to make out anything other than grey shapes that looked more like bats than birds. Louisa walked with him to his car. There was a chill in the air and he thought some years there was no real summer at all.