‘That’s him,’ said Bailey. She nodded at Dylan, who was currently standing on the other side of the visit hall.

‘That’s Dylan?’

Frank surreptitiously studied Dylan, sizing him up with a professional policeman’s eye.

‘Go on then,’ he said. ‘Convince me. And it had better be solid.’

She glanced around to check no one was listening and leaned forward across the table. She laid out everything in a low urgent voice, explaining how she’d progressed from Sharon to Agata, and then from her to Dylan, describing in detail her subsequent encounters with him, along with a summary of her chat with Doctor Bodie.

Frank listened without interrupting, occasionally nodding as he did so. When she had finished, he sat there looking down at the table, mulling over what she had said. She waited tensely for his approval. He finally looked up at her.

‘So you’re basically saying that he’s this Jekyll and Hyde character who’s reliving some kind of battle trauma when he’s committing these crimes?’

‘I think he’s capable of doing very bad things. When he talked about Afghanistan, he implied that he did the same things to the enemy as they did to his fellow soldiers. He mentioned mutilation and cutting off body parts.’

‘Did he explicitly state that he took scalps?’

‘No, but I think it’s highly plausible that he did.’

Her most recent conversation with Doctor Bodie, combined with her insights into Dylan’s military past, had reinforced her belief in his culpability.

‘You’re just speculating now,’ said Frank. ‘Like you were before, with the Hairdresser.’

She found his scepticism frustrating but not unexpected. Frank had never been a fan of hunches.

‘But you have to admit it makes perfect sense when you consider his background and the nature of the crimes being committed in here. And it’s all backed up by Doctor Bodie’s explanation. And you yourself checked the rota – he was on duty when all four of them were murdered.’

‘I find it hard to accept that someone who has been committing these kinds of crimes would also be able to sustain what is basically a regular sexual relationship with one of the inmates.’

‘That’s my whole point. One part of him is conducting a normal relationship with Agata, but another completely different part of his personality is doing the murdering and the scalping.’

Frank frowned and chewed on one of his fingernails. She could tell that he wasn’t convinced.

‘I don’t think he’s completely aware that he’s doing it,’ she said. ‘That’s because this other sub-personality takes control of his behaviour when he—’

She felt Frank suddenly kick her under the table. She broke off and glanced around. Dylan was approaching their table on his circuit of the visit hall. He walked slowly past. As he did so, she looked up at him. He smiled pleasantly at her, the tanned skin around his pale blue eyes crinkling in that distinctive way. He nodded politely at Frank and continued past their table.

They waited until he was out of earshot.