When Bolt walked in, Marie was laughing at something Turner had said, and he almost felt as if he was interrupting something. They both stopped speaking and turned his way, and Marie looked a bit sheepish.

'Andrea's gone to lie down,' he told them with a smile to show he hadn't seen or heard anything untoward.

He took the coffee cup from Marie and added a couple of sugars to it. There was another photo of Emma attached to the cupboard above the kettle, this time just a snapshot. In it she was flanked by her mother on one side and a lean, good-looking guy with unkempt brown hair on the other. They looked like a typical family. It made Bolt feel slightly jealous, although he wasn't a hundred per cent sure why.

'Do you think the husband's involved, sir?' asked Turner, seeing Bolt looking at the photo.

'Part of me says definitely,' he answered quietly, aware that he had to be careful what he said in front of Marie, who wasn't officially part of this inquiry, 'because it would explain how the kidnappers knew Emma's movements. But the other part says that if he is, why on earth did he then disappear? Surely he'd have known it would only arouse suspicion. It'd be far better to let the kidnappers know when and where to make the snatch, then act completely innocent. Even if we suspected him, there'd be nothing we could do about it.'

'That's what I was thinking,' said Turner. 'It's all wrong somehow, isn't it?'

Bolt was about to tell him not to speculate too much out loud when he heard a rapid set of footfalls on the stairs, and Andrea came rushing into the room dressed in a full-length dressing gown, her mobile phone in her right hand.

'They've called.'

'When? Just now?'

'Yes. On the mobile.'

'What did they say?'

'He asked if I was getting the money together for tomorrow night. I said I was, and he told me to turn my computer on and check my emails.'

She took a deep breath, and Bolt could tell she was using all her strength to hold things together.

'They said they've sent me a warning.'

While Andrea fetched her laptop and turned it on, Matt Turner called in to HQ and asked them to run an urgent trace on the last number to call Andrea's mobile. 'They'll get back to us in five,' he said as he and Bolt followed Andrea through the hallway and into a large, spacious study at the back of the house.

Andrea set the laptop down on a desk at the far end of the room which faced out on to the back lawn, and sat down to wait while it booted up. Bolt and Turner stood behind her while Marie Cohen remained further back, in the doorway. The desk itself was expensive mahogany and scrupulously tidy. There were two framed photos on it: one of Emma as a toddler, dressed in a pink swimming costume and playing with a hosepipe, laughing at the camera; another more recent one of mother and daughter smiling.

'What do you think they mean by sending me a warning?' asked Andrea, turning round in her seat and looking up at Bolt.

'Let's just see,' he said calmly.

'That's easy for you to say, isn't it?' she snapped, turning back and double-clicking on her internet icon.

Bolt didn't answer. The problem was that he wasn't very good around victims of crime. He never had been. He much preferred the process of detective work, of breaking up criminal enterprises. Of identifying targets and hitting them. He might have suffered his own private tragedy but the fact remained that he wasn't trained for this, and being intimately acquainted with this particular victim wasn't helping either. He looked over at Marie Cohen, wondering if she was going to intervene with soothing words, but she remained silent, motioning him just to leave it.

Andrea's homepage appeared on the screen and she clicked on her emails. There were a dozen or so unread messages but it was the one at the top, sent from a numbered hotmail account, which was the one they wanted. The word WARNING was written in block capitals in the subject column, and there was an mpeg attachment.

Without speaking, Andrea opened it. The message said simply WATCH THE FILM.

'Oh God,' she whispered.

Bolt tensed. 'Maybe it's best if we watch it first, Andrea,' he told her, putting a reassuring hand on her shoulder. He didn't add 'just in case', but he knew he might as well have done.

She took another deep breath. 'No. She's my daughter. I've got to watch it.'

'It might not be a good idea, Andrea,' said Marie, moving into the study.

'I am going to watch it. End of story.' Her words were loud and decisive, cutting across the room.

She clicked on the mpeg file and waited the twenty seconds while it downloaded. The room was silent, with just the peaceful sound of birdsong coming from outside. With trembling fingers, Andrea pressed play.

Immediately the screen was filled with the top half of a person sitting against a wall in a darkened room lit by a bulb somewhere off camera. The quality of the recording was very good, and Bolt knew that he was looking at Emma even though she had a black hood over her head. The arms beneath the black T-shirt she was wearing were pale and skinny – kid's arms.

Andrea let out an audible gasp.

For two or three seconds Emma sat there, absolutely still, then very slowly she lifted a copy of The Times until it was in full view. The main headline was about the run on the Northern Rock bank. The camera panned forward until it was fixed on the date in the top right-hand corner. It was today's.

'See, Andrea, she's alive,' said Bolt, trying to sound positive. 'And it's in their interests to keep her that way.'

Andrea didn't reply, but her shoulders were shaking, and he realized she was crying silently as she stared at the screen.

The camera panned back so that Emma's upper body filled the screen again, and then the camera suddenly jerked as the cameraman reached forward with a gloved hand and roughly removed the hood, revealing the pretty teenage girl with the dark blonde hair and blue eyes whose photo was all over Andrea's house.

Her face was terrified and wet with tears as she stared uncertainly at the cameraman. He appeared to give her some sort of off-camera prompt because she started to speak slowly and carefully, her voice shaking with fear. 'Mum, they say that if you get the money, they'll let me go tomorrow night.' There was a pause again while she appeared to get a second prompt. 'But Mum… they said that if you don't pay, or you call the police… they said they'd hurt me really bad.' As she spoke these last words, the tears began streaming down her face again.

Then she gave a short, tight gasp. She was staring at something they couldn't see, her eyes widening.

'Oh God, Emma,' whispered Andrea, her own voice cracking under the strain. 'My darling.'

And then they all saw it. The long, gleaming blade of a hunting knife, held in a black-gloved hand, moving slowly across the screen from right to left, mocking the viewers with its presence. It belonged to the cameraman. His camera shook very slightly as he moved it. The knife then changed direction as he leaned forward, pointing the tip of the blade at Emma's neck. His arm beyond the glove was covered by a black sweater. There was no flesh showing, nothing that might even hint at a possible ID.

A torturous wail came from Andrea. 'No, Jesus, no. Please. Don't hurt her.'

Bolt felt his mouth go parchment dry. This was total sadism, something that, thank God, was rare.

In twenty years of law enforcement he'd only seen something similar once before when he'd been forced to watch an old amateur videotape showing the sexual abuse and torture of a three-year-old child by her father. That was a long time ago now, yet he could still remember every single moment of it. It was etched on his brain, like a hideous tattoo, for ever. This was similar, and in a way all the more painful in that the victim's mother was someone he'd once cared so much for.