Alex and Chloe sat in the incident room looking once more at the gallery of faces pinned to the evidence board. They were out of time, and with nothing substantial with which to charge Isobel Matthews, they’d had to let her go. The knowledge smarted. The team was working at maximum capacity to make contact with the people who’d been at the party that night and reassess the CCTV footage from the area, but hope of finding any evidence that way was wearing thin. It was impossible for them to account for every person who might have been at the house at some point during the evening on the night Keira North died.

‘What was she like when you spoke to her?’ Chloe asked. ‘Leah’s mother?’

Alex had spoken with Kimberley Cross after her phone conversation with Carol Brooks. Kimberley had been able to fill in the missing details of Leah’s past, citing behaviour Alex found entirely believable given the nature of the young woman they had encountered.

‘She didn’t sound surprised by what’s happened. Do you think she had any idea what her daughter was up to, pretending to be another woman’s child?’

Alex shook her head. ‘Seems she washed her hands of her a while back. By all accounts, Kimberley did everything she could for her after Leah’s father died. By the time she hit her teens, her mother was already struggling to handle her.’

‘If she was so difficult to manage, why would Carol Brooks offer to have her stay with her family?’

‘I wondered the same,’ Alex said. ‘According to both mothers, Carol’s daughter Kirsty and Leah were close throughout secondary school and Leah was very convincing when it came to her version of events. She told people she was neglected, that her mother drank too much and didn’t care about her. She played the innocent victim very convincingly.’

‘Not difficult to believe. We’ve seen how good she is at that.’

‘Exactly. Kimberley admits she had her problems. Her husband died when Leah was seven – he was killed in an accident at work. She told me she didn’t cope well after his death; said she never really recovered from it. She said Leah seemed to resent her and the relationship just got worse over time. Apparently after her husband’s death a tribunal decided that the accident had been avoidable and had been caused by personal error, so the company never had to pay out any compensation. The couple were young and he had no life insurance. Kimberley worked two jobs to try to keep afloat, but being out so often meant Leah had free rein to run off the rails. By the time Leah went to stay with Carol, Kimberley was getting therapy for depression and addiction to prescription medication. She admitted all this freely. She said Carol was trying to help her. Carol told me she’d done some fostering in the past, but she bit off more than she could chew with Leah.’

Chloe shook her head. It was difficult to comprehend how such kindness had been repaid with such deceit. ‘How did Leah find out so much about the relationship between Carol and Leighton?’

Alex shrugged. ‘Both mothers said how close the girls were, so I suppose they talked a lot. They had the fact that they were both missing their fathers in common. Kirsty’s stepfather, Jonathan, has been in her life since she was five, but Carol told me she’d always been honest with her about how she was conceived and why she didn’t know her real father. Let’s remember that Leah was living in the house too – it was easy for her to gain access to photographs of Carol with Kirsty as a baby.’

Chloe shook her head again and studied the image of Leah pinned on to the evidence board. ‘Clever,’ she mused. ‘Very clever.’

‘Not so clever she didn’t get caught out.’

‘Think the same will apply to Isobel?’

‘Our best option at the moment is to keep applying the pressure. We get someone who claims to have seen her at the party and we bring her back in. She’ll cave in eventually. There’s also the knife to consider. It’s still with forensics, but once we get it back, we can make a start on finding out where it came from.’

Chloe stretched her legs in front of her and stifled a yawn. ‘Do you think Leighton ever questioned Leah’s surname? Surely he must have wondered why it wasn’t Chambers, or Brooks?’

Alex shrugged. ‘She’s an expert liar. She knew enough to convince him, I suppose. He knew what he’d done all those years ago; he wasn’t prepared to risk losing everything.’

‘What do you make of Leah trying to kiss Leighton? No wonder that was a shock for him, given that he still believed she was his daughter.’

‘I don’t know. The boundaries have all become so blurred, I doubt she knows why she did it. Maybe she’s attracted to him. Maybe she felt a different kind of bond developing. I think she came to South Wales with a cash cow in mind, but Leighton perhaps became something more. He seems to have some inexplicable appeal to younger women, though God knows why. Whatever happened, Leah is one very troubled girl.’

‘What was the final straw then?’ Chloe asked. ‘What happened that made Carol Brooks so reluctant to even acknowledge Leah?’

‘She stole Kirsty’s university savings,’ Alex said, standing from her chair. ‘Over three thousand pounds, apparently.’ She tilted her head to one side, easing the tension in her neck. ‘Come on, let’s call it a day. We’re not going to achieve anything by sitting here wondering what’s gone on in the mind of that girl. We’d be here until Christmas.’

‘How soon do you reckon we can get Isobel back in?’

Alex glanced at her watch. ‘We’ll try again tomorrow, but we’ll need to be careful. If the Matthewses start shouting harassment, Harry’s going to be straight on to us. I still think if we keep pushing hard enough, Isobel will break. Right – home time.’

Alex headed back to her office to retrieve her things, arranging to meet Chloe in the car park. When she got to reception, however, she was intercepted by a flustered-looking desk sergeant, accompanied by a couple of the night-shift officers and a civilian dressed in a supermarket uniform.

‘This lady says she’s just witnessed an attack out on the street.’ The sergeant gestured to the woman in the supermarket uniform. ‘Apparently a man hit a woman and bundled her into his car.’

‘There’s no apparently about it,’ the woman said defensively, as though the desk sergeant thought her drunk or mad. She waved an arm in the direction of the main doors. ‘I just watched him doing it.’

‘Thing is,’ one of the officers said to Alex, ‘this woman … it sounds as though it might have been Isobel Matthews.’