Mick and Colin burst in, all-business. They sat down and began reading material without saying a word. I saw Laura glancing sideways at her solicitor. He raised his eyebrows as if to say: ‘Fucked if I know.’

This was it: our one-and-only chance to nail Laura. She had lied consistently to protect Karen, and possibly to avoid incriminating herself. One thing was certain: Laura knew a lot more than she was saying about Marion Ryan’s murder. But we had nothing on her. Unless she slipped up now, or broke down and confessed, she’d walk out of here for the last time. She could even get her sister off the hook, if she put on a good show.

After what seemed an age, Mick put his papers down and whistled lightly, as if to say: ‘I’ve got all I need now.’ Without signal, Colin turned on the tape recorder, announcing the time and guests.

Mick opened with the afternoon of the murder. Just like her older sister, Laura couldn’t remember any of the boutiques they’d browsed in Blackheath. They’d clearly thought it through: shops have CCTV.

Laura repeated her alibi as if by rote: returned to the Pines after five, met Bethan Trott in the communal kitchen, watched TV until six when Karen left to service the home’s fish tanks with Peter. They let her regurgitate the entire story, confidently and at length, without mentioning that it had now been completely discredited by the only independent witness – Bethan Trott. I hoped that, sometime soon, a jury would get to decide which of these young women was telling the truth.

Mick tried a fresh tack: ‘Have you ever been to Marion’s flat, Laura?’

She shook her head.

‘The client has shaken her head to indicate a negative to the question. It’s better if you speak, Laura, so that we can get it on tape.’

‘No,’ she said, sullenly.

‘No what, Laura,’ sighed Mick.

‘No, I’ve never been to Marion’s flat.’

‘Do you know where it is, Laura?’

‘It’s in Clapham somewhere.’

‘And how do you know that?’

‘How do you think I know?’ she sneered, then screwed up her face in disbelief at the question. ‘Karen used to go there all the time, to see Marion and Peter.’

Colin sprang to his feet, spun away and prowled the top of the room. He composed himself, sat back down and took over.

‘Karen’s obsessed with Peter Ryan, isn’t she, Laura?’

‘No, she isn’t.’

‘She moved out of your family home and into staff accommodation at the Pines a month before his wedding to Marion, didn’t she, Laura?’

‘Yes but …’

‘In a last-ditch attempt to win Peter Ryan, wasn’t it?’

‘No.’

‘To stalk Peter, spy on Peter, tempt Peter.’

Laura’s face reddened.

‘No.’

‘So that Peter could have her any time he felt like it.’

‘No,’ shouted Laura, ‘she moved out because of my dad.’

‘Oh come along now, Laura. You don’t expect us to believe that.’

‘My dad, when he gets drunk, he can get … aggressive.’

‘Really? The police haven’t been called to your home. Doesn’t sound like the violent type to me?’

‘He’s different when he’s drunk. He’s attacked us all, loads of times.’

‘Attacked?’ sneered Colin.

‘Karen used to stand up to him, to protect me and Stacey. That’s when he turns into an animal and beats the hell out of her, smashing her head into the wall and all sorts. When she got a chance to move into a room she could afford, we persuaded her to go for it. By then, me and Stacey were old enough to look after ourselves. Sometimes, when Dad’s drinking, I go and stay with Karen. I’ve got a spare key.’

Shep got to his feet and walked to the glass. ‘I wonder what else Karen had to protect her pretty little sister from? Their dad, Terry, probably wasn’t attracted to Karen, so moved straight on to Laura. I’ve seen it before. That’d partly explain Karen’s crippling insecurity, and Laura’s blind loyalty. Lynch, as soon as we’re finished here, call up Terry Foster’s previous, and find out if social services have taken an interest.’

As usual, Colin and Mick seemed to be thinking along the same lines.

‘So, you’d describe yourself as a loyal sister?’ asked Colin.

‘Yeah, of course,’ she said, frowning in disdain at the question.

‘She took a few beatings for you, did she, Laura?’

‘Yeah, quite a few actually.’

‘It’s fair to say you feel a sense of debt to Karen for this?’

Laura nodded.

‘Can you please speak?’

‘Yes I do.’

‘So when she asked you to come with her, to confront Marion, you weren’t really in a position to say no, were you, Laura?’

‘Like I said, I’ve never been to Marion’s home.’

‘You thought she was only going to tell Marion about the affair, maybe scare her a little. But then it all got out of hand, didn’t it, Laura?’

‘No comment,’ said Laura. I noticed she wasn’t looking at Colin or Mick now. She’d picked a spot on the far side of the room and was focusing on that. I’d read about this in one of my correspondence classes: a classic anti-interrogation technique, used by IRA suspects and the like. It made her look as guilty as sin. But no jury would ever see this – only sound was being recorded.

‘And now you’re going to get done for murder as well, Laura, as an accessory. You know why, because you’re not taking this chance to tell us the truth? What do you say to that, Laura?’

‘No comment,’ she said, unblinking, spectral.

They needed to get her talking again, or all was lost.

‘Well guess what, we know the truth. We’ve got evidence putting you at the scene.’

Laura’s stare faltered for just a nanosecond, then refroze.

‘You’ll go down for life, Laura, don’t you understand? Twelve years in Holloway prison. That’s what you’re facing. Is that what you want?’

‘No comment,’ said Laura.

Colin sat back and took a deep breath. Shep pressed his forehead against the two-way. ‘This is it,’ he said to the glass, ‘last throw of the dice.’

Colin began gently: ‘You know what they hate most in prison, Laura? Nonces. You know, paedophiles, child molesters, perverts who target children. Did you know that?’

‘No comment.’

‘Do you know what they hate most after nonces, Laura? They hate child killers. Especially people who kill really young kids.’

Laura just glared at that spot, her brain in auto-focus.

‘You did know Marion was pregnant, Laura?’

She stiffened, then shivered, losing her focus spot on the wall. This was it: if she was ever going to break, it would be now.

After a series of sharp breaths, Laura turned to her solicitor and whispered something.

He spoke up. ‘My client is feeling unwell and would like some fresh air. And I really must object to this tone of questioning.’

Mick told the tape recorder the news and shut it down.

‘Fuck,’ screamed Shep, butting the glass, ‘that’s all our ammo gone. She’s never gonna break now.’

A uniformed WPC walked into the suite and signalled to Laura and the solicitor to come with her. The solicitor ushered Laura to the door first. It was then that I spotted just how garish her trainers were. They had a quirky blue and green, cross-strap design on the side that reached above the ankle and bright green soles. I’d only been off the streets a few weeks but I’d never seen a pair like it, even at our Nike trainer identification seminar last year. I couldn’t help thinking: what delicious irony if she got stabbed for them.

I walked out to the corridor just as Laura was being led past. I took a closer look at her shoes: they were Nike, but not the much-stabbed-for Air Jordans. The WPC led them to the security door that divided the interview suites from the main block. Laura’s idea of fresh air clearly meant a Superking in the car park. The WPC hit the green release button, pulled the tightly-sprung door open towards her and walked through, making just a token effort to hold it for Laura.

Feeling the weight of the door, Laura instinctively turned her back against it to keep it open and signalled for her solicitor to walk through next. But he was lumpen, meaning that Laura needed to push the door back further so that he could get past. She achieved this by planting the sole of her trainer against the door and pushing her foot back. While doing this, she turned and looked directly at me.