It started with Stephanie Slater, her bravery as she lay alone in the dark, injured and terrified. To Robin, she became a hero, a symbol of strength, and when the Wests and their house of horrors came to light, Robin had an epiphany: that was what she wanted. She wanted strength. She wanted to be a hero. She wanted to break down the door and rescue the next Stephanie Slater. She wanted to be the one who followed the Wests home, kicked Fred in the bollocks, and pulled the girl away from the car, the teetering edge of the void.

That was what she told anyone who asked why she’d decided to go into the police. Over the years, she’d made it sound more and more ridiculous – Behold the high-kicking, karate-chopping teen ninja girl! Marvel at the self-importance, the naivety! – but it was true; it had been the first reason before she had another.

Maggie hadn’t followed the Slater case in the news: she’d worked on it. Not immediately, on the original core team, but as soon as the investigation started to expand. Unsurprisingly, it loomed large in her memory. She’d kept quiet at Valerie’s, of course, but in the car on their way here to the office, she’d brought it up.

‘Kidnap for ransom? Really?’ Robin was dubious. Nothing about the Woodsons’ set-up said money, and Valerie’s only real savings, she’d told them, were in a small private pension that wouldn’t mature for another seventeen years.

‘Remember the Slater case?’ Maggie said. ‘It was her employers, the estate agents, that Sams went after – he wanted their insurance money. Valerie might not have much but Becca works for a silversmith.’

Hanley’s. Battered floral address book in hand, Valerie had given them the number. ‘They make photo frames and candlesticks,’ she said. ‘Hip flasks and the like. Corporate gifts.’

‘They’d have had a demand by now, wouldn’t they?’ said Robin. ‘Thursday to Tuesday – five days?’

‘Yes. Unless …’ Maggie had glanced across. ‘Julie Dart.’

Mentally shafted as she was, it had taken Robin three or four seconds to connect the dots. Then she did.

The investigation into Sams had expanded beyond Stephanie Slater. Based on similarities in the two cases, West Yorkshire Police believed that a year earlier, in Leeds, he had abducted another woman – if woman was the word. Julie Dart had been just eighteen when he’d taken her, a kidnapping ‘dry run’ that went wrong; she’d managed to escape from the coffin-sized box and he’d returned to find her desperately trying to get out of his workshop. He’d killed her.

‘If there’d been a demand, we wouldn’t be on the case, obviously – the police would be all over it,’ Maggie said. ‘But if something went wrong, he – or they – might not have got that far. He might have killed her, jettisoned the plan, like Sams did.’