Patrick told Carmella to take the car and called a taxi for himself. While he waited he took the printout with Fredericks’ details from his inner pocket and scanned through it. Her psychiatrist’s name was Dr Catherine Hudson.

Patrick called the secure unit and asked to speak to Dr Hudson, but was told she’d gone home for the day.

‘It’s extremely urgent,’ he said. ‘Can you give me her phone number?’

After a few minutes of arguing about confidentiality, the receptionist agreed to give Dr Hudson Patrick’s number, and would ask her to call him. He had no choice but to agree.

Ten minutes later, his phone rang. Finally, someone who didn’t enjoy obstructing the police. Dr Hudson told him she was at home and that she would be happy to talk to him there.

Her house was a five-minute drive away, not far from Helen and Sean’s place. Another detached property with a ridiculous price tag. Not for the first time, as he waited for the psychiatrist to come to the door, Patrick muttered to himself that he was in the wrong game.

Two minutes later he sat in Dr Hudson’s home office, surrounded by stacks of paper and hundreds of academic books with titles that made his head hurt. Dr Hudson was a good-looking black woman in her late forties, with smooth skin and an amused look in her eyes.

‘Thank you so much for agreeing to talk to me,’ he said.

He wondered if she knew the connection between them. There were a lot of doctors at the secure unit, and Dr Hudson probably wasn’t treating Gill, but there was a good chance this woman had encountered his wife or at least knew of her. He decided not to bring it up.

He explained that he was trying to find Sharon Fredericks.

‘I know there are proper channels, and that you’re probably going to cite patient confidentiality, but I’m going to be open with you. I’m investigating the so-called Child Catcher case—’

Dr Hudson’s eyes widened.

‘—and this is very urgent. I need to find Ms Fredericks ASAP, so we can eliminate her from the enquiry.’

Catherine Hudson perched on the edge of her desk and ran her forefinger across her chin thoughtfully. ‘Hmm. Well, yes, there is patient confidentiality, of course. But I couldn’t help you with her whereabouts anyway. I referred her on to another practitioner very shortly after she was discharged. Someone who I thought could do more for her.’

‘Can you give me their name?’

She rocked her head from side to side and said, ‘Hmmm.’

‘Come on, Dr Hudson . . . please?’

Without replying, Hudson went over to her vast bookcase and scanned the shelves. ‘Uh-huh,’ she said to herself, taking down a thick book with a white spine and laying it on the desk.