Bowie stared at the floor. ‘No. Because then Mum got back and she had ice lollies and everyone went a bit crazy. I mean, even crazier.’

‘And what about the woman. Would you recognize her?’

‘I think so.’

‘Could you describe her? I don’t mean right now – I mean, if you sat down with an artist, could you tell them what the woman looked like so they could draw her?’

‘I could try. She had sort of frizzy dark brown hair. She was short.’

Patrick smiled. In every investigation, you need a break, a stroke of good fortune. This could be his: finding the most observant seven-year-old in London.

He addressed Liza. ‘I’d like you and Bowie to come down to the station so he can sit with a sketch artist. It’s important to do it as quickly as possible.’

‘That’s fine. I just need to get someone to babysit. I’ll go and ask Sandy next door.’

She zipped out of the room, towards the front door, and Patrick found himself sharing an uncomfortable silence with Bowie. The boy stared at the rug and Patrick groped for a topic of conversation that this kid might be interested in. Cars, that was it. But then he couldn’t think of anything to say about cars. He was still fishing about in his head when Bowie said, ‘I expect he’s dead.’

Patrick looked up.

The boy glanced at the window to see if his mum was coming back. ‘The lady who took him. My brother said she’s a witch. She steals kids, sucks their life from them, then dumps their bodies.’

‘No, that’s not—’

‘And now I’ve told you I’ve seen her, she’ll come for me.’ His voice trembled but Patrick could sense he was trying to be brave. ‘Please catch her, Detective. Before she gets me.’

Patrick stared at the computer, his head filled with the image of a witch with yellow, gluttonous eyes and a mouth full of sharp teeth designed for tearing and chewing children’s flesh. A woman. Bowie had said that Liam had been taken by a woman, and he was in with the sketch artist now, describing her. The news had raced around the station like chicken pox round a nursery.

And he’d said that Liam hadn’t been scared, had looked at her like he knew her. He picked up the sketch Frankie had made of the face at the window (the witch?) and asked himself, again, why the Philips girl hadn’t cried out or told her sister about it.