‘I did, and again she insisted that it wasn’t her. She was adamant that she’d always chosen a different location to push people in, and she had a reason for that. She wanted the people of Cork to come to believe that nowhere along the riverbank was safe. Living by the Lee is one of the things that makes Corkonians happy, she said. It was her intention to make them dread the river, to the point where they might even move away from Cork altogether. She said she wanted the Lee to be more frightening than the Styx.’

‘What’s your professional opinion, then? That it really wasn’t her who killed Roisin Carroll?’

Dr Power was about to carry on, but hesitated, and looked across at Detective O’Donovan as if she wasn’t sure what she should say next.

‘It’s okay, doctor,’ he told her. ‘You’re grand altogether. You can tell DS Maguire about it. I don’t think she’ll be after giving you a hard time for it.’

‘If you’re sure,’ said Dr Power. ‘What I did was kind of illegal, and it certainly wouldn’t stand up in court. The thing was, Doireann’s solicitor asked if we could have a five-minute break because she needed to use the toilet and make a couple of phone calls to her office. So while she was out of the room, I hypnotized Doireann.’

‘You hypnotized her? You can actually do that?’

‘I did a study on hypnosis at Trinity a couple of years ago. I was trying to evaluate how effective it is as a medical treatment. At the time I interviewed several famous stage hypnotists like Keith Barry and I also talked to Martin Keiller, who runs a hypnosis clinic here in Cork. Between them they taught me how to put people under, and it’s not as difficult as you might think.’

‘You’re absolutely right, though, about it being “kind of illegal”,’ Katie told her. ‘We have fierce strict rules about questioning suspects. Only two gardaí are allowed to question a suspect at any one time, and only three are allowed altogether into the interview room. Hypnosis – well, that’s totally out of the question. Even if Doireann admitted under hypnosis that she’d pushed a hundred more victims into the river, as well as fifty dogs and ten babies, I couldn’t possibly use that as evidence. Quite apart from the fact that her solicitor was out of the room.’

‘I told her to fix her attention on one of my earrings, and she went under just like that,’ said Dr Power, snapping her fingers. ‘But – she wouldn’t admit to killing anybody else. In fact, she stuck to her original story, word for word.’

‘You don’t think she was codding you? You know – pretending to be hypnotized?’