Cooper glanced nervously around again. If back-up was going to arrive.

‘Yes. We just came together for this one purpose. It was almost random. We talked to each other all the time on those walks. We talked like I’ve never been able to talk to my dad.’

‘They were loyal too,’ said Cooper.

‘You’re right. They were. None of them gave away the fact that I was there at the bridge, did they?’

‘No. We accepted your story completely.’

‘Thank you.’

She spoke as if it were a genuine compliment.

‘So what did happen at the bridge?’ asked Cooper.

‘It was bad luck. The fact is, Sandra was out of control that night. I don’t know what she was on exactly, but she was totally out of her head. She began to run around in the woods like a crazy woman. Then she came after me and chased me towards the bridge. She scared me. I thought she was going to do me some harm. God knows what she was thinking, but I’m sure she was hallucinating. The others had no idea what was going on, though. We were supposed to be quiet and not draw any attention to ourselves. When they heard all the commotion they didn’t know what to think.’

‘They imagined someone else must be there,’ said Cooper.

‘Yes, exactly.’

‘And that would have ruined the plan.’

Cooper felt his phone buzz in his pocket. He reached for it slowly, but Poppy backed away again and he lost sight of her in the shadows.

‘Sandra caught me near the bridge,’ said Poppy. ‘I seriously thought she was going to do something bad to me, she was so nuts. I think I must have screamed. Jason says he heard a scream anyway. I suppose that must have been me. Though Sandra was making plenty of noise too, crashing about in the trees. But then she seemed to start coughing or choking and she fell on the ground. I had no idea what to do. I thought she was still messing around.’

‘And no one came to help you?’

‘Yes, Jason did.’ Poppy moved her head sideways so that he couldn’t see her eyes. Was she looking towards someone who stood in the darkness? Or was the gesture merely theatrical?

Cooper moved too, trying to maintain eye contact. Perhaps he ought to arrest her right now. But what had she admitted to, really? Perverting the course of justice? Conspiracy? There wasn’t much of a case against her. He needed to know more.

‘It was lucky I wasn’t relying on Rob,’ said Poppy. ‘He’s not the bravest of people.’

‘What happened to Sandra?’ persisted Cooper.

Poppy sighed. ‘She should never have come out with us on something like that. We didn’t know she had a heart condition.’

‘I don’t think she knew either.’

‘If she had a family history of heart disease, she ought to have gone to her GP for a review. I bet she was a prime candidate for heart disease. A bad diet, smoking, too little exercise, a family history…’

‘So. At some point on this particular evening she simply dropped down dead in front of you,’ said Cooper.

‘Pretty much.’

‘And what did you do?’

‘I’ve got to admit, I had no idea what to do. I was about ready to panic, to be honest. But Jason said he’d done a bit of first-aid training. He tried CPR. You know, pressing on her chest, mouth-to-mouth, and all that.’

‘But no one called an ambulance, did they?’

‘No. Well … no, we didn’t.’

Cooper was silent for a moment. ‘No matter how long Mr Shaw performed CPR, it was pretty useless without defibrillation, which is what actually restarts the heart.’

‘That’s what I said to Jason. I mean, we both knew that Sandra was dead. It was so obvious. There was no way she was going to be brought back to life. Right in those first few seconds, she was dead. She was already a ghost.’

Cooper shivered at her choice of phrase. The factory had made him feel uneasy as soon as he’d entered it. If your imagination ran in that direction, you might think there were phantom presences here, the spirits of the former occupants imprinted in the walls. But his senses were warning him of whispers and movements in the darkness. He couldn’t tell yet whether they were real or illusory.

‘We both panicked a bit, then,’ said Poppy. ‘Jason had touched her hat and her torch, so he took those away with him, in case of fingerprints. Then we rolled her body off the bridge. Her head hit the rocks, which was a bit nasty. But she wasn’t feeling any pain by then, was she?’

She was actually appealing to him for reassurance.

‘No, Poppy,’ he said.

‘It was funny, but it was only when I got home that I thought about her mobile phone. But it must have been in the river, I suppose. I dropped my phone in water once. It didn’t work too well after that.’

Cooper took a cautious step towards her, but she noticed and backed out of the light. That was worse. Now she was almost invisible and he was the one standing directly beneath the opening, bathed in the odd light. He could see the green tinge on the skin of his hands, like the discoloration of flesh after death.

‘Poor Jason was upset,’ said Poppy. ‘He was quite keen on Sandra. He likes them a bit weird, I think.’

Cooper could have kicked himself as he listened to her story. He’d noticed all those people coming forward and telling him part of the truth, as if they’d been told to do that. The Nadens, Jason Shaw, even Brendan Kilner. But he’d never thought to himself: And what about Poppy Mellor? She’d come forward voluntarily and appeared to be a willing witness. But she’d only told part of the truth too.

Yes, she’d been clever in some ways. Yet she was so young, so inexperienced about life. And about people too.

‘And George Redfearn?’ he said.

‘Unfortunate. But it was just like Sandra’s death.’

‘No.’ Cooper shook his head. ‘You can see a heart attack coming. It’s there in the tests. It’s in the blood. But this is different. You don’t see a murder coming.’

‘Sometimes you can.’

‘But it wasn’t you who killed George Redfearn, Poppy. That’s something I can’t believe.’

‘Can’t you, really? But it’s so easy, isn’t it? To get someone up on a high place like that and shove them off. You don’t need much strength.’

‘No, that’s true.’

And he had to admit it was true. A quick push, a momentary loss of balance. He’d imagined it himself on the sharp ridge of Parkhouse Hill just yesterday.

But Poppy was still backing away from him as he crossed the walkway.

‘You are right, though,’ she said.

‘Right?’

‘It wasn’t me. I was back home by then. You can check with my dad, if you want. He’ll be only too happy to talk to you.’

Cooper held his breath, listening for a sound, any sound, in the darkness. He was beginning to feel disorientated by the blackness all around him. His eyes couldn’t adjust because of the light he was standing in. He felt like a character on a stage, pinned by the spotlights, and about to perform his big scene in front of an audience he couldn’t see.

‘You’re a different person from the one I met before, Poppy,’ he said.

‘I was in character before.’

‘I’m sorry?’

‘I took a joint honours in drama studies at De Montfort,’ she said. ‘I wasn’t great. But good enough.’

Poppy was backing away steadily and Cooper had to follow to keep her in view.

‘And you coached the rest of your group, didn’t you?’ he said. ‘They all played their parts well. Congratulations.’

‘Thank you,’ said Poppy again. Then she paused. ‘But the final act isn’t over yet, I’m afraid.’

Cooper found himself at the foot of a flight of metal steps leading up on to an overhead walkway. It might once have passed over the cheese vats, but now there was nothing but a bare concrete floor below.

He thought he saw Poppy’s pale figure above and ahead of him, and he mounted the steps on to the walkway.

‘Where are you?’ he said.

But the voice came from behind him.

‘I’m here. Very close.’