‘Then leave everything in the car—wallets, bags, the lot.’

‘But . . .’

‘Be quiet and listen. Until we get back here, your names are Tom Southwell and Jessica Whiteley. You’re both here for a job interview—English teacher, education department. You handed over your passports this morning—they’ve got them—and you’ve just nipped out for lunch. Right?’

I’m about to tell her I can’t do it when I hear Saul say, ‘Right.’ I make a face at him behind Charlie’s back, but he doesn’t notice. He’s busy mouthing, ‘Tom Southwell’ to himself.

When we reach the glass-sided hut that’s set into the high wire-mesh fence, Charlie says her name with confidence, for our benefit as well as that of the uniformed guard inside. ‘You’ve got my ID already. There I am.’ She points to her name on his list. ‘Oh, it wasn’t you before, was it? Sorry.’

‘No probs.’

‘Same with us,’ says Saul easily. ‘Tom Southwell and Jessica Whiteley.’

‘In you come,’ says the guard. He has to unlock three gates for us. Charlie tells him we know where we’re going and he leaves us to it.

‘Where are we going?’ I ask.

‘Patience, Ruth,’ says Saul. I give him a look. He’s the one who’s supposed to dislike surprises; he’s all talk.

‘To the education department,’ says Charlie.

‘I don’t want to teach English in a prison,’ I tell her. ‘What’s going on?’

Eventually, we come to a wide corridor with green-painted walls. I think of the last time I followed Charlie down. It feels like a lifetime ago. Like that one, this one has pictures on the walls, the prisoners’ artwork, some of it excellent. Charlie stops in front of a picture, and when I look at it, my heart surges up to fill my throat.

‘Her,’ I say, feeling the same horror I’d feel if she were to materialise in front of me, back from the dead. I’d recognise her style anywhere. I recognise the picture, too, from Aidan’s description.

‘We were right,’ says Charlie. ‘I’m sorry. I know it’s a shock, but you had to see it. I couldn’t not show it to you. We were right, and my boss was wrong. Ex-boss,’ she corrects herself.

‘The Murder of Mary Trelease,’ I say. ‘So she did do a copy. But . . . how did it get to be . . .?’

‘She visited Smith in prison,’ says Charlie. ‘It occurred to me on the way here that she might have. Why wouldn’t she? She wanted to get close to Aidan in any way she could, as long as it wasn’t too risky. She knew Aidan didn’t see Smith or have any contact with him. She couldn’t resist.’

‘You mean . . . you asked Len Smith . . .?’