‘We’re fine now,’ Mitchell said.

‘Three bloody buses and a train to get out to Hatfield,’ Collins said. She shook her head, disgusted. ‘You’d think the council would lay on some sort of transport, wouldn’t you? But they’re too busy funding lesbian play centres and that sort of shit.’

‘We don’t mind,’ Mitchell said. ‘It’s always an adventure, providing the weather’s OK.’ She looked round at Kitson. ‘He doesn’t get bored like other kids, you know?’

‘Is it autism?’ Kitson asked.

Mitchell shrugged. ‘They don’t think so. I don’t think they know what it is, tell you the truth, and we’ve given up worrying about it. Whatever it is, nobody can do anything about it, so we just get on with things.’

Thorne watched as the boy pushed his train back and forth, his chin quivering as he made barely audible ‘chuffing’ noises. He had the same wide blue eyes as his mother, though his lips were fuller, redder. When he smiled, which for no reason that was obvious he did every minute or so, his front teeth slid down over his bottom lip and he moved them quickly from side to side. There was no way of knowing if Debbie Mitchell did the same thing, as Thorne had yet to see her smile.

‘How much does he understand?’ Thorne asked.

Nina Collins was lighting up again. ‘Bloody hell, are you pair coppers or social workers?’

‘I just don’t want to upset him,’ Thorne said. ‘When we get started.’

Mitchell shook her head, like it was OK, but her hand drifted across to her son’s head, moved through his hair.

‘You going to tell us about this man again?’ Collins said.

Thorne nodded. ‘What have they told you so far, the sensitive coppers and the shouty ones?’

Mitchell took a deep breath. ‘They talked about this weirdo who might want to hurt me because of what happened to my mum.’

Thorne nodded again. ‘Right, and they probably said stuff like, “We have reason to believe that you might be in danger.”’

‘Something like that.’

‘Well, here’s the thing. There’s no might about it, OK? Not if you stay where you are.’

Kitson moved her chair forward. ‘You mustn’t underestimate the man we’re talking about here, Debbie.’

‘She’s had weirdos like this floating around all her life,’ Collins said. ‘Wanting to know about what happened to her mum, getting some cheap thrill out of it or something.’

‘This particular weirdo has already killed four people, Debbie,’ Thorne said. ‘Four people whose mothers died the same way yours did.’

Collins’ hand was in her hair, pulling at the spikes. ‘They never said four…’

‘A couple, I thought,’ Mitchell said. ‘You know, that might have been by this same man.’

Thorne looked at Kitson. He wondered who had taken the decision about what this woman should be told. Had they deliberated over how many previous murders they could mention? Was two deemed to be OK and three unacceptable? It seemed ridiculous, not least because one should have been enough to send anyone scurrying for cover without looking back. But whatever was preventing Debbie Mitchell from doing the sensible thing, and however much trouble he might be in for taking a unilateral decision, Thorne could see no point in pussyfooting around.

‘Would you like to know how he did it?’ Thorne asked.

‘No.’ Collins had gone noticeably pale.

‘Exactly how he stalked and murdered four people, what he used to kill them. Would that make you take this seriously? Get you off your arse and make you start packing?’

‘It wouldn’t make any difference,’ Mitchell said, raising her voice. ‘We need to stay here.’

The women had moved even closer together. Thorne could see that Jason had stopped playing with his train and was on his knees by the side of the sofa, pulling at his mother’s hand, trying to rub it against his cheek.

‘Are you worried about Jason?’ Kitson said. ‘Is that the problem? Because you wouldn’t be separated.’

Mitchell started shaking her head, but it wasn’t clear if she was answering the question or just didn’t believe what Kitson was telling her.

‘We have special accommodation designed for families.’

‘No.’

‘You need to get out-’

‘He got into their houses,’ Thorne said. ‘Don’t you understand? They all thought they were safe and he got inside and murdered them.’

‘I’ll look after them,’ Collins said.

Thorne flicked his eyes to her. ‘What, even at night, Nina? You’ll be working, won’t you?’ Thorne had checked Collins’ record and seen that she’d had more arrests for soliciting than Debbie Mitchell. He watched her blink, glanced across in time to see something pass across Kitson’s face, and felt a stab of guilt; felt the wind leak out of him. However stupid and stubborn these women were being, it was clear that Nina Collins was hugely attached to Debbie Mitchell and her son; that her affection for them was fierce and unconditional. ‘Look, I’m just saying…’

When Collins came back at him, her voice had dropped a little. The nerves were evident in the staccato drags on her cigarette and the stutter as she blew out the smoke. ‘Can’t you look after us?’

‘That’s what we’re trying to do,’ Thorne said.

‘We can’t go,’ Mitchell said. She was staring at Jason, watching the teeth move across his bottom lip as he squeezed her hand. ‘You don’t understand. He needs routine. We both do. It’s the only way we can manage to keep everything on an even keel, you know? The only thing that stops it all going to pieces.’

In the desperation that had masked her face, Thorne caught a glimpse of what was driving her. He could see that her terror in acknowledging the threat – the crippling fear of change that could see a spiral back into drugs and might conceivably cost her custody of her child again – was even greater than her fear of the man who wanted to kill her.

‘He would be so unhappy,’ she said.

Thorne understood, just, but it didn’t matter. ‘How happy would he be if you were dead?’

Mitchell suddenly cried out in pain and yanked her hand away from Jason’s mouth, her knuckles having caught on the boy’s teeth as he squeezed and kissed it. His face was frozen for a few seconds in shock and she quickly got off the sofa to comfort him, but he was already starting to whimper and turn back to his plastic train.

Collins stood up too. ‘That’s enough, I reckon,’ she said. She waited for Thorne and Kitson to get up, then ushered them towards the front door.

Kitson stopped and turned at the end of the hallway. ‘Please try and talk some sense into her, Nina.’

Collins reached past her and opened the door. ‘What would make sense is for you lot to stop pissing about and catch this nutter. All right, love? Then we wouldn’t need to be having this conversation, would we?’

‘For Jason’s sake,’ Thorne said.

Collins all but pushed them both out on to the front step and stared Thorne down, her swagger returned. She said, ‘I liked you better when you were telling your shit jokes.’

Then she slammed the door in their faces.

‘Looks like it’s got to be an arrest then,’ Kitson said, as they walked towards the car.

Thorne shook his head and moved quickly ahead of her. ‘Last chance,’ he said. He opened the door of the BMW, reached inside for a large brown envelope and walked back past Kitson, towards Debbie Mitchell’s front door.

‘Tom…?’

He said nothing when Nina Collins opened the door. Just pushed the envelope into her hand and wheeled away. He was halfway back to the car when he heard the door close behind him.

Kitson stared at him as he turned the ignition over. ‘Was that what I think it was?’

‘Impossible to answer that,’ Thorne said. He held up his hand to stop her speaking again, as if it might help the engine catch. ‘I have no idea what you think it was.’