‘He’s not exactly a baby, is he?’ Holland leaned forward, dropped a hand on to each of the front headrests. ‘They were probably just waiting for him to come waltzing back home again.’

‘That’s more or less how they explained it.’

‘He might have done this sort of thing before.’

‘No, I don’t think so,’ Porter said. She took the unmarked Saab Turbo past a silver 4×4, glared hard at the driver, who was talking animatedly into her mobile phone. ‘But like I said, we haven’t spoken to the parents that much yet. Hopefully we’ll find out a bit more over the next couple of hours.’

‘Presuming we get there in one piece.’ Thorne was sitting a little stiffly in the passenger seat, unnerved to discover that Porter was just as impatient behind the wheel as she had been back in the office. Her frequent glances into the rear-view mirror had more to do with the purpose of their journey than it did with road safety.

‘Obviously, any kind of threat and we wouldn’t be interviewing the family at home. We’d stay well clear; find some way of talking to them on neutral territory.’

‘That can’t always be easy,’ Holland said.

‘It isn’t, but if you have to visit the home address, there are ways and means. You just need to be a bit inventive.’

‘What, like disguises and stuff?’

Thorne turned, and pulled a face at Holland. ‘Disguises? How old are you, six?’

‘Right,’ Porter said. ‘We’ve got a big dressing-up box back at the office. Gas Board uniforms and postmen’s outfits.’ She took a long look at the rear-view. ‘There’s no reason to believe that visiting the Mullens at home places Luke in any kind of extra danger, but there are procedures you follow whatever the circumstances. You make sure the lid stays on. You make sure there’s no uniformed involvement.’ Another check in the mirror. ‘And you keep your bloody eyes open.’

The crash course in kidnap investigation techniques had lasted from the car park at the Yard as far as Arkley – a leafy Hertfordshire suburb a dozen or so miles north of the centre of London. It had become clear that the unit’s protocols were infinitely flexible and that everything happened much faster than elsewhere. Though kidnapping was little different from murder – in that the unit would never have any such thing as a ‘typical’ case – Thorne was surprised at the enormous range of crimes that fell within its remit. Though the majority of kidnaps were subject to a press blackout and so never became public knowledge, there could be no doubt that it was a growth industry.

‘And a relatively safe one for the kidnappers,’ Porter said. She told them that over half of all her cases involved hardcore foreign drug gangs, distributors and smugglers; that fewer than one in five ever resulted in a conviction. ‘Most of the victims never testify, the ungrateful fuckers. We rescued an old guy last year who’d been tied up in a loft and tortured for a couple of weeks. They cut both the poor bastard’s ears off and he still wouldn’t give evidence in case others in the gang came after him.’

‘You can understand him being scared,’ Holland said. ‘He wouldn’t hear them coming.’

Thorne sighed, shifted in his seat. ‘Sounds like you’re all getting plenty of overtime,’ he said.

Porter grunted her agreement. ‘Heavy-duty dealers are getting lifted every other week. Yardies, Russians, Albanians, whatever. It’s a quick way of scoring cash or merchandise – putting the shits up a rival. We’re not short of jobs, but maybe the wheels don’t turn quite so quickly when it comes to some of our less than law-abiding kidnap victims.’

Thorne knew very well what she meant. He’d worked on a case the year before; the case during which his father had died. The squad, and Thorne in particular, had found themselves caught in the middle of a vicious gang war. He explained to Porter that one side had been involved in a people-smuggling racket; that though a fair number of gang members had died, few could bring themselves to care a great deal, or argue that the city wasn’t a better place without them.

‘That stuff’s down to us, too,’Porter said. ‘If people are brought here and then used as slave labour, they’ve basically become hostages. They’re held against their will and usually there’s an implied threat to their families back at home.’ She slowed the car to a stop a hundred yards from a driveway. ‘It’s also the main reason why people are queuing up to work on the unit,’ she continued. ‘So far this year I’ve been to China, Turkey, the Ukraine. It’s all business class, and we get the air miles.’

Holland sucked his teeth. ‘I went to Aberdeen to interview a rapist once…’

Porter took a good look at a Jag that drove past, waited a minute or two after it had disappeared around a corner, before moving the Saab slowly forward and turning it on to the driveway.

‘This kind of case isn’t common, though, is it?’ Thorne asked. ‘Snatching civilians?’

She shook her head. ‘You can get the family of a bank employee being held until the safe’s opened, but even that’s pretty rare. You might get one like this in Spain and Italy every so often, but it’s like rocking-horse shit here. Thank God.’

‘So why no ransom with Luke Mullen?’

‘I’ve no idea.’

‘I still don’t see why it has to be a kidnap.’

‘It doesn’t. There are other possibilities.’

‘Like Luke going off voluntarily with the woman in the blue car?’

‘Or just running away,’ Porter said. ‘But parents never like to admit that their precious kid might do that.’

Holland released his seatbelt. ‘Like no parent ever thinks their kids are stupid, or ugly.’

‘You’ve got kids?’

‘I’ve got a little girl.’ Holland grinned. ‘She’s gorgeous and very bright.’

‘Maybe this isn’t about money at all,’ Thorne said.

Porter appeared to think about it as she killed the engine. ‘It’s certainly… unusual.’

‘Who knows…’ – Thorne opened the door and swung his legs out, let out a groan of pain as he lifted himself upright – ‘if there had been a ransom demand, maybe the parents might have got on the phone a bit quicker.’

Holland got out and walked towards him, looking up at the detached, mock-Tudor house where Tony Mullen and his wife lived. ‘It’s a big place,’ he said.

Porter locked the car and the three of them began moving together towards the front door. ‘It’s probably feeling that little bit bigger just at the moment,’ she said.

A few minutes earlier, Thorne had seen the relief flood into Tony Mullen’s face, but it had been purely temporary. Already, sitting across from Thorne in an uncomfortable-looking armchair, a damp pallor of desperation was smearing itself back across his features; the look of a man bracing himself.

He’d been at the front door before they were, staring out at the three of them as if he were urgently trying to read something in how they walked; to work out what they had come to tell him by the way they approached the house. Porter had shaken her head. A small movement, but it had been enough.

Mullen had let out a long breath and closed his eyes for a second or two. There was something approaching a smile when he opened them again, when he moved the hand that had been flat and white against the door frame and held it out, palm skyward, towards them.

‘Your guts just go into your boots,’ he said. ‘Whenever the phone goes or the bloody doorbell rings, especially if it’s you lot. It’s like feeling the punch coming. You know?’

The introductions were made there on the doorstep.

‘Trevor Jesmond said he’d sort out a few extra pairs of hands,’ Mullen said. He touched Thorne’s arm. ‘Make sure you say “thanks” to him, will you?’

Thorne wondered if Jesmond had told Mullen what he really thought about the man those extra hands belonged to. If he had, Thorne guessed it was probably a less than honest assessment. If the request for help had come directly from Mullen himself, Jesmond would hardly want his old friend thinking he was palming him off with damaged goods. Thorne decided it was a subject best left alone; that he should keep things light for as long as it was appropriate.