‘We’ll get that arranged as soon as we can,’ Holland said.

Parsons made a note of the boy’s name and address. They asked him a few more questions: ascertained exactly where he’d been standing the previous Friday afternoon; how far away he’d been; if there was anyone with him at the time.

‘People have been saying that she was Luke’s girlfriend or something,’ the boy said out of the blue, ‘but I can’t say I’m convinced.’

‘Why not?’ Holland found it hard to believe that the boy could be an expert on such matters; that he was much beyond a crush on the dinner ladies.

‘Body language.’ He said it as though it were obvious, and as if he were becoming slightly bored with the conversation. Yet there was an authority and a confidence about him, which, to Holland at least, made what he said oddly credible.

‘What about Luke? What did he seem like?’

‘Happy enough, I suppose. They walked straight past me at one point and he was talking to her.’

‘Did you-?’

‘I didn’t catch any of what was said I’m afraid, but he seemed… content.’

‘It didn’t look like he was going anywhere under duress, then? He didn’t seem frightened or apprehensive?’

‘No, but she did.’ The boy swung his briefcase distractedly. Stared past Holland and Parsons towards the school gates, as if he were looking for a friend. ‘She looked scared to death.’

Thorne had certainly made good use of his Travelcard.

He’d been across to Barking to talk to a DI on the Intel Unit based there, then spent an hour and a half travelling up to Finchley to interview a DCI on the Flying Squad. Both men had told him what a great bloke Tony Mullen was, what a loss it had been when he’d retired so early, how terrible it was that his family had been targeted. One of them said he’d started a collection at the station, but then stopped and given the money back when he’d realised he didn’t know what it was for.

They had looked at Mullen’s already truncated list. Neither had made much comment, but each had told a war story or two, remembering the part they’d played alongside Tony Mullen in catching and putting away the individuals named. Thorne had listened, laughed in all the right places, and encouraged each officer in turn to consider any other of Mullen’s past cases that they felt might have a bearing on what was happening. To give him the name of any person they felt should be checked out, if only to be eliminated from any enquiry. Between them, another two names had been suggested; four altogether now on the list Thorne carried with him on the short journey to Colindale. To the meeting he had scheduled at the Peel Centre.

In the Major Incident Room on the third floor of Becke House, Thorne spent fifteen minutes catching up with a few of those he would normally have been working with: he shared a quick cup of coffee with Yvonne Kitson, who seemed a little preoccupied; he traded jokes with Samir Karim and Andy Stone, who assured him that no one had even noticed he was gone; and he stuck his head round Russell Brigstocke’s door in the vain hope of some moral support.

Detective Chief Superintendent Trevor Jesmond made it clear from the second Thorne stepped across his threshold that they were not going to be talking for long.

‘It shouldn’t take long, Sir.’

‘Good. I’m up to my bloody eyeballs.’

Thorne brought Jesmond up to speed on the Luke Mullen case as briskly as he could. He explained that they had to seriously consider revenge as the motive for kidnapping Tony Mullen’s son; that they were looking at anyone who might be holding a grudge. As Jesmond knew Mullen better than anyone, Thorne said, and had worked closely with him over a number of years, nobody was better placed, or better qualified, to cast an expert eye across a list of the candidates. He laid it on good and thick, and though Thorne could see that Jesmond knew he was being flattered, it seemed to work.

‘Naturally I’m keen to do anything I can to help,’ Jesmond said.

Thorne reached into his pocket for the list. ‘Of course…’

‘Tony and Maggie are going through hell.’

‘A couple more names have been added since we spoke on the phone…’

Jesmond stood and walked past Thorne to the door. He lifted an overcoat from a metal hat-stand. ‘We’ll continue this outside. Then I can be doing other things at the same time.’

‘It’s still not a long list-’

‘What is it women like to say? That we blokes can’t multi-task?’

Thorne said nothing, alarmed to see Jesmond’s thin lips sliding back across his teeth in something approaching a smile.

One of the ‘other things’ turned out to involve trudging across to the centre’s driving school, where, for no obviously good reason, they stood and watched those on the advanced driving course take cars around the track or turn inwards to career across a skid-pan.

Jesmond waved to one of the instructors, then shouted above the roar of an engine: ‘Do you like motor sport, Thorne?’

Thorne pretended he hadn’t heard, and asked Jesmond to repeat the question while he thought about whether to lie. He watched an Audi squealing between a series of bollards. ‘Only the crashes,’ he said.

And that was the end of that.

The driving school was directly opposite the athletics arena. When not captivated by the sight of cars swerving or being driven at high speed, Thorne could glance across and watch a gaggle of recruits jogging slowly around the asphalt perimeter. Each wore a pristine blue tracksuit, but several looked anything but athletic. Most looked as though they’d have preferred a nice riot, or maybe an armed siege.

‘Tony Mullen had a decent strike rate,’ Jesmond said. ‘As good as anyone I can think of, as it happens. But you know as well as I do that most of the lowlife we put away treat being caught as part of the job. They don’t take it personally. If they were going to try and get their own back on every copper who’d ever nicked them, they’d be far too fucking busy to reoffend.’

Thorne knew it was true, by and large, but he also knew better than most that there were some to whom the rules did not, could not, apply. When it came to the ones that killed, there were some for whom the offence was far from occupational; whose reactions when they were caught – when they were no longer able to act on their compulsions – were anything but predictable.

It was clear when Jesmond spoke again that, as usual, the expression on Thorne’s face had made it obvious what he was thinking.

‘Of course, there are always going to be headcases,’ Jesmond said, ‘and I know you’ve had your fair share of those over the last few years. But they can usually be discounted, because the majority of them end up in places they’re never coming out of again.’

The majority of them.

A few names and faces flashed through Thorne’s mind: Nicklin, Foley, Zarif…

‘Thorne?’

Thorne nodded, not quite sure what he was being asked. To his right, a mud-spattered meat wagon moved slowly through the car wash. Three more brooded in line behind it.

‘Let’s have a look at this list, then,’ Jesmond said.

Thorne passed the slip of paper across, waited.

‘I wouldn’t even think about Billy Campbell.’ Jesmond jabbed at the paper. ‘He was just a gobshite. Told just about every copper, judge and prison officer he ever ran across that he’d come after them. Liked to shout his mouth off, that’s all, same as a lot of them.’

Campbell’s was one of the two names added that morning. Thorne hadn’t had a chance to run it through the system. ‘What about the others?’ he asked.

‘I’ve never heard of Wayne Anthony Barber.’

The other new name. ‘Went down on two counts of rape in 1994. Liked to threaten his victims with a screwdriver. Went for Mullen in the interview room, by all accounts.’

Jesmond shrugged and pointed to the two names at the top of the list. ‘These the ones Tony Mullen gave you?’