He pressed call-back but it said her phone was switched off, which seemed odd if she was so keen to get hold of him. He sighed, hoping she hadn't got herself into trouble, knowing it wouldn't be the first time. Tina had a habit of relying heavily on her initiative and being prepared to go it alone on investigations, and occasionally she wasn't very good at judging when to stop. The positive side to this was that she usually got results. But, he thought grimly, it wasn't always such a positive if she was out there alone, dealing with the wrong kind of people.

'Anything the matter, boss?' asked Mo as they got back to the office.

'Nothing exciting,' Bolt replied, unsure about how much to tell Mo, who'd never got on that well with Tina, and who probably wouldn't approve of him encouraging her to follow up on her leads.

Although the team worked in an open-plan office, Bolt had his own small room at the far end. He went in there now and tried Tina's number a second time. Still switched off. He sat back at his desk and opened up his email screen on the PC.

There were ten new messages from various people, which was about average, but straight away he saw that the most recent one was from Tina, and that it had been sent just ten minutes ago. He opened it and read the message: Do you recognize this man?

There were five photos attached. He double-clicked on the first one. It was a profile shot of a man in a cap and sunglasses. The quality was good – Bolt could see that the skin on his pale face was tight, as if he'd had plastic surgery – but the subject was clearly well disguised. The second shot was similar but with less of the subject's face showing. The third was of the back of a Toyota Land Cruiser on a residential street. He took down its registration number, wishing Tina had given a bit more of an explanation in her email as to what this was all about. Then he opened photo number four.

This one was a close-up, full-frontal shot of the man in the cap and sunglasses from the chest upwards. He was trying to keep his head down and wasn't looking at the camera, but even so, there was something familiar about him. Bolt expanded the photo until it filled the screen, then focused on the pale face. It looked like the man had suffered burns at one time because the plastic surgery looked more like repair work than anything cosmetic. He zoomed in on the chin. The quality got worse, the picture beginning to blur, but a rectangle of skin lined with scar tissue remained distinctive. It was about half the size of a credit card and much fainter than it had been before, but unmistakable nonetheless.

Bolt felt a physical jolt. He took a deep breath and zoomed out again so that he was back to just the face. 'Jesus, it can't be,' he whispered. 'Not you.'

He turned away from the screen and called out to Mo.

'Is this who I think it is?' he asked, turning the monitor round as Mo came into the office.

Mo stared at the picture for a long time.

'It's him, isn't it?' said Bolt, zooming in again and pointing out the scar.

'It is,' said Mo at last. 'It's Hook. Who sent you this?'

Bolt's throat felt dry as he answered. 'Tina Boyd. About ten minutes ago. I'm guessing she was the one who took the photo.'

'Have you spoken to her yet?'

Bolt shook his head. 'No. Her phone's switched off. I just tried it.'

'Do you know when she took it?'

'No, but I'm guessing it was probably today. And here in London.'

Mo whistled through his lips. 'So Hook's back in town. There's got to be a very good reason why he'd risk his neck to be back here.'

Bolt dialled Tina's mobile again. It was still off.

'Well, whatever it is,' he said, 'I'm truly hoping he hasn't crossed paths with Tina. Because if he has…'

He let the sentence trail off. They both knew all too well what Hook was capable of.

Tina stared straight ahead as she drove through the streets of Hackney in the direction of the A12, as per the gunman's instructions, making absolutely sure that she avoided any eye contact, not wanting to give him an excuse to put a bullet in her.

She was trying to remain as calm as possible but it was damn hard, and she could feel herself sweating as she tried to figure out how to get out of this situation. She'd been in tight corners before, facing the wrong end of a gun, and had come out of them in one piece, but there was no guarantee that it would happen again, and she had a very bad feeling about the man next to her. Most criminals, even the well-organized professional ones, tended to exhibit signs of nerves, particularly when they were pointing a gun at someone, but this guy was sitting there with an almost Zen-like calmness, and in Tina's experience that made him extremely dangerous.

She stopped at a busy junction as the lights went red. Outside the car window the street was thronged with passers-by swarming around one another like ants, only feet away, yet as good as a million miles. No one looked at Tina, or caught her eye. A group of schoolchildren crossed in front of the car, one of them scraping his bag against the bonnet. They were so close she could hear their banter – heard one of them call his friend a name. She tensed, looking for the right moment to make her move.

'I know what you're thinking,' he said, and once again his thick Northern Irish accent sounded strange to Tina. It didn't really fit with the delicate, almost feminine features of his face. 'You're thinking that now's a good time to make a break for it. That I won't dare shoot you in broad daylight with a lot of people around. And I can understand that. But I'm afraid you'd be making a big mistake. You'd never even get a hand on the handle before I put a bullet in your heart. The rounds in this pistol are low-velocity so there'd be no exit wound, no smashed windows. And, with this suppressor, no noise. You know how impersonal London is, the way its citizens hurry on by minding their own business. I guarantee no one will have any idea that you've just been murdered.'

Tina didn't say anything. He'd read her thoughts. The lights turned green, and any chance she'd had (and in truth there had been none) was gone. She pulled away, indicating right.

'So, pretty lady, who are you? And what were you doing taking photos of me?'

She knew she was going to have to play this carefully. If she said the wrong thing, she was dead. 'My name's Tina Boyd, and I'm a police officer.'

'And what were you doing on that street? You can't have known I'd be coming by, so you must have been there for a reason. What is it?'

Tina knew there was no point lying. Not now. 'I was watching a property.'

'Ah, the one belonging to our friend Mr Gentleman, I'll wager.'

'That's right.'

'Interesting.'

'Look,' she said with as much confidence as she could muster, 'you may as well give yourself up. It's the best way.'

The man let out a low chuckle, his lips hardly moving. 'Now why would I want to do that? You appear to be unarmed and in no position to threaten me, and any colleagues you might have don't appear to be – how shall I put it? – beating a path to your door.' He turned round in his seat and looked through the back window. 'Do they?'

Again, Tina spoke with a confidence she didn't feel. 'My colleagues know where I am and they're on the way.'

'Is that right? And is it them you were talking to on your mobile phone just now?'

'Yes, so I really wouldn't do anything stupid. They'll throw away the key if anything happens to me.'

'I think, my love, that they would throw away the key if they caught me anyway. I've already killed one person today.' Out of the corner of her eye she could see him regarding her, his thin lips forming a tight smile. 'Our mutual friend, Mr Gentleman. How long do you think I'll get for snuffing him out?'