‘But they could have. You were at school with him, and we both know some of his old uni friends, past flatmates, or colleagues he’s mentioned. I’m sure if we start digging … maybe the police have missed someone? And no one knows Luke like we do; we’d have a better idea if, say, something was mentioned that sounded off about his past behaviour, or if they said something that didn’t fit with what he’d told us. And at least we’d be doing something. I feel like we’re going slowly insane here.’

He pulled on his lip. ‘That’s true.’

‘Will you help me?’ She looked at him beseechingly until he sighed.

‘OK. If it’ll make you feel better, sure.’

She smiled. ‘Good. We need to make a list of people to approach. Ex-girlfriends from school and uni, old flatmates and female friends, women he used to work with – before Brindle, I mean. Anyone at all that he might have got on the wrong side of, or who might know of someone he fell out with at some point.’ She pulled out her phone. ‘Get your laptop. Let’s start with Facebook.’

For more than an hour they sat side by side in silent concentration. It was slow work: Miles, a friend from Luke’s uni days, was still in touch with the sister of Luke’s ex-girlfriend Jade. Andrew, who once worked with Luke at the digital publishing company he’d been at before Brindle, was Facebook friends with a woman who’d been on his team there, who herself still kept in contact with a couple more of their female colleagues. Yet despite the difficulty of their task, for the first time in days Clara felt a sense of purpose, and bit by bit a list of women began to emerge.

‘I’m worried this could be a massive waste of time,’ Mac said.

‘Keep going,’ she replied, her eyes still on her phone. ‘At least it’s a start.’

They were about to take a break when Clara noticed the New Message symbol on her Facebook page. She frowned in confusion when she saw she’d been contacted by someone calling themselves ‘Rumpelteazer’. But when she read the message, she felt the hairs on the back of her neck stand up. ‘Oh my God!’ she shouted.

Mac looked up in alarm. ‘What? What’s happened?’

Wordlessly she handed him her phone. The message had been sent from a locked account, with a blank Profile picture. Mac read it out loud.

‘“Clara. I saw you on the news. I’m Luke’s sister Emily Lawson. It’s very important you don’t tell my family I’ve contacted you. Do not tell the police. Can we meet?”’

Mac’s mouth fell open in shock. ‘No way,’ he said, as he looked from the message to Clara’s face then back again. ‘No way that’s her …’