‘Hang on, you weren’t the one who ignored them. You never even knew about them.’

‘I’ll find out who did ignore them, but that’s not the point. Whoever it was, they looked at that piece of information and dismissed it, presumably because it sounded like bollocks. Within the general framework of the case, the direction we were moving in, they looked like crank calls.’

‘The obvious route is usually the right one, Yvonne.’

‘Well, it wasn’t this time.’ Kitson had lowered her voice, but now it was growing louder, more strident. ‘We had our heads up our arses, and when a posh public school four or five miles away was mentioned, it was ignored because we thought we were looking in the right place. Because we were far too busy talking to kids at the comprehensives in the shittier parts of Edgware and Burnt Oak. Knocking on every door on the Deansbrook estate, and on the Wallgrove…’

Andy Stone came round the corner and Kitson trailed off. Stone nodded at the two of them, non-committal, and walked away again after a second or two. Thorne thought that Stone wasn’t the greatest copper he’d ever known, but every so often his instincts were spot on.

Kitson spoke quietly again. ‘Now that kid can afford to be a cocky little sod, because he knows he’s got away with it. Because we let him. He can swan around, wearing the same earring he wore on the night he killed Amin Latif, because he thinks he’s bulletproof.’

An officer by the lift kicked the doors, then walked briskly past them towards the stairs, announcing that he couldn’t be bothered to wait, that he was desperate for a fag.

‘I know all about fucking up,’ Thorne said. ‘I’ve done stuff that makes this look trivial.’

That got something to soften around Kitson’s eyes. ‘I’m not arguing,’ she said.

‘There wouldn’t be any point.’

‘I just want to put this right.’

‘Well, that’s the good part. Unlike most of the times I’ve fucked up, it sounds like you’ve got the chance.’

Now that they were out of the more dangerous territory, they returned to the lifts.

‘Bearing in mind how we came across Farrell in the first place, are we chasing up a possible link to this case?’ Kitson pressed the button. ‘We’re sure that he knows Mullen at least.’

Considering the strange turn that the case had taken in the previous twelve hours, Thorne now thought it even less likely that there could be a connection between the kidnapping of Luke Mullen and a six-month-old racially motivated murder. But he also remembered what he’d just said to Kitson about the most obvious route. ‘It can’t hurt to talk to him when you get the chance,’ he said.

The lift arrived and they stepped inside.

‘I certainly plan on getting the chance,’ Kitson said. ‘But he’s not the easiest kid to talk to.’

‘How are your three, anyway?’

The doors slid across as an officer from Serious and Organised slipped quickly inside. Kitson answered Thorne as though she were measuring her own children against others she might recently have met.

‘Fucking gorgeous.’

On the ground floor, Thorne’s phone rang as he moved gingerly through the revolving doors.

‘This is Graham Hoolihan. You left a message…’

Hoolihan was the DCI whose details had been passed on by Carol Chamberlain. He had led the investigation five years earlier into the murder of Sarah Hanley, believed to have been killed by her boyfriend, Grant Freestone. Thorne had left Hoolihan a message the previous afternoon.

‘Thanks for getting back to me so quickly,’ Thorne said. ‘I don’t know if Carol Chamberlain explained why we’re interested in Grant Freestone…’

She had, but evidently it hadn’t been to Hoolihan’s satisfaction. So Thorne went over it again. Outside Scotland Yard, the pavement was thick with people on their way to work, hurrying towards Parliament Square and Buckingham Gate. Though the rain had as good as gone, there were still one or two umbrellas up, as it looked like it hadn’t gone very far.

Hoolihan did not know Tony Mullen, and was unaware of any threats that might have been made against him by Grant Freestone. He was sure about one thing, though: ‘Freestone’s not a kidnapper.’

Thorne was consistently surprised by how ready people were to put criminals into boxes. Lazy or just unimaginative, it seemed strange to him. If a seemingly respectable doctor could be a serial killer in his spare time, why was it so difficult to conceive of a paedophile and suspected murderer kidnapping someone? ‘Did you know him?’ Thorne asked.

‘I never met him,’ Hoolihan said. ‘Though I hope to have that pleasure one day.’

‘I hope you do, too.’ Thorne marked down the man on the phone as one of those who hated to fail, but guessed that it was the result – or the lack of one – more than any sense of injustice that needled him. Points or passion; it usually came down to one or the other.

‘You could try talking to one of the people on Freestone’s MAPPA panel. They ought to have known the bastard. They watched him for six months after he came out, didn’t they?’

‘Thanks, I’ll do that.’

‘I can’t tell you who they were, mind you, except for the copper who was involved. I dug his name out before I called.’

Thorne reached into his jacket pocket and scribbled down the details on the back of a used Travelcard. ‘He’d have the names of the others on the panel, would he?’

‘I’ve no idea,’ Hoolihan said. ‘We certainly didn’t have anything to do with them at the time. We just wanted to find Freestone. Once he’d buggered off, a bunch of social workers, or what have you, was no use to anyone. The whole thing was a waste of bloody time, if you want my honest opinion. Do-gooders who didn’t really do a fat lot of good!’

‘Why “do-gooders”?’

‘They decide to tell Sarah Hanley about Freestone. About what he’s like. They then tell Freestone what they’re going to do, so he goes marching round there, him and Hanley argue, and he throws the poor cow through a coffee table.’

‘You think it was the MAPPA panel’s fault that Sarah Hanley was killed?’

Hoolihan paused, unwilling perhaps to go quite that far. ‘The “PP” is supposed to stand for “Public Protection”…’

The chat didn’t last much longer, with both men keen to get on with their days. Afterwards, Thorne sat on one of the concrete bollards and made four phone calls trying to get hold of DCI Callum Roper. Once he’d tracked down his quarry, he made an appointment to see him later that morning. During their brief conversation he outlined the Mullen case, taking care to drop the names Hignett, Brigstocke and Jesmond, and to stress the urgency of the situation. He never mentioned Grant Freestone.

Then he began heading towards Westminster tube station, exchanging nods with an armed officer he knew by sight. He watched as a kid with a Mohican posed next to the officer while his mate took a photo. The copper smiled politely and put a hand on the kid’s shoulder. The kid grinned like an idiot and pointed towards the copper’s machine-gun. Thorne turned at the clatter of heels on the pavement behind him.

‘Hold on…’

Porter caught up, fell into step beside Thorne, and the two of them carried on walking. They had not spoken since the cursory exchanges the night before, at the crime scene.

‘You move pretty fast for a short-arse,’ she said.

They carried on in silence past Christchurch Gardens, originally part of St Margaret’s, Westminster and burial site of the seventeenth-century Irish adventurer Thomas ‘Colonel’ Blood, who stole the Crown Jewels. In point of fact, Blood was buried twice, his body having been dug up by those keen to make sure that he was really dead before being interred again. Thorne had known one or two villains himself, happily no longer walking around, who it might have been worth checking up on…

‘Thanks for speaking up at the briefing,’ he said.