They sat down on the couches under the windows and Moirin came in to ask them if they would like coffee or tea. Katie couldn’t help noticing that the hooded crows were still crowded on the rooftop opposite. Usually, when it was raining as hard as this, they flew off to find shelter under the roof of the Merchants Quay car park. When they stayed, it almost always meant trouble.

‘I questioned her again and again, using several different approaches. First I was gentle with her, and sympathetic. Then I was remote and made out that I wasn’t particularly interested in what she had to say. That technique often works with psychopathic subjects like her. No matter how much they say they hate the world, and don’t care about it, they’re desperate to be heard and understood.’

‘What results did you get from that?’

‘Only the same answer again and again. “I pushed the first six into the river, but not the seventh.” “I wasn’t there on that afternoon, I swear it. I was tucked up in bed with the terrible cramps.”’

‘So where did you take it from there?’

‘I really gave her down the banks. You were seen! I told her. You were seen by the old fellow who saved that poor woman’s baby from drowning! Do you seriously think he wouldn’t recognize you? In fact, I got so angry with her that her solicitor told me to ease off and treat her more gentle. But of course I was only putting it on. I was trying to rile her into shouting back at me. I wanted to provoke her into admitting that yes, she had pushed Roisin Carroll into the river, and she was only denying it to show the rest of the world that she could stick up two fingers to us and there was nothing we could do about it.’

‘But if that’s the way she felt, why didn’t she deny the other six murders? Why only that one?’

‘That’s exactly what I asked myself, DS Maguire. Why only that one? And with that one, there was an interesting anomaly. All of the other times she’d pushed somebody into the river, she’d done it at a different location. But this one was at precisely the same spot as the previous incident – The Marina, midway between the rowing club and the park.’

‘Did you ask her about that?’