Simon stood up and moved his chair further away from Isobel’s. Sitting down again, he said, ‘I don’t get it. Help me. You kill five people – I reckon you were planning on Kim too, so let’s say six. One’s been involved with your brother so there’s a connection there, but why the others? What links all six? Something must.’

‘I can’t tell you anything!’ Isobel screamed. Coming from her silence, it was more shocking, like a small earthquake in the room. Simon saw Sam flinch. He’d done the same himself.

‘I haven’t murdered anybody, but I can’t tell you … I just can’t tell you.’

‘Why not?’ Simon asked.

‘Because then everything would be ruined,’ she said.

‘This is the first time I’ve been here in a few days,’ Lisa Norbury told Sellers. They were in Josh’s flat in Spilling, in the large L-shaped kitchen. Sellers was sitting at the breakfast bar and Lisa stood at the kitchen sink, looking out over the large shared garden. Sellers had met her only once before, immediately after her brother’s murder. She looked much thinner today, and the skin of her face seemed somehow to have the wrong texture, as if she’d exchanged it for its synthetic equivalent.

She wasn’t holding up well, that much was clear. She was supposed to be making Sellers a coffee but had got no further than the window. It looked as if she’d forgotten. She reached out to pick up a cocktail shaker from the windowsill, then put it down again.

Josh had been something of an amateur mixologist, and this room had accommodated many a cocktail party. Before Billy and this investigation, Sellers hadn’t known the word ‘mixologist’. His two teenage children had laughed at him when he’d asked them if they knew it. ‘Of course, Dad. Everyone knows that!’ They’d then proceeded to test Sellers on other modern terms they suspected he’d be unaware of: bae, beasted, pwned.

‘I keep thinking, if I can stay away one day longer each time …’ Lisa laughed self-consciously. ‘I feel awful when I don’t come, though. It’s like the flat’s become a substitute for Josh. If I don’t come, it’s like I’m not visiting him. Crazy.’

‘Not at all,’ said Sellers. ‘For what it’s worth, I don’t think you should try to stop yourself if your instinct is to be here more often. Whatever makes you feel better.’

Lisa nodded. ‘Josh was killed a month ago. I keep worrying that I ought to be getting over it faster.’