Walking past the huge statue of Abraham Lincoln, Porter pointed back to the windows on the third floor of the Guildhall. ‘His office was fucking horrible,’ she said. ‘Did you see the damp? And the mousetrap by the filing cabinet? I’d go mental working somewhere like that all day.’

Thorne said nothing, thinking she did work somewhere like that. All of them did, spending endless hours in other people’s houses and shitty little offices. TV shows were fond of showing coppers, and those they needed to speak to, strolling slowly through the crowd at noisy dog tracks, arguing in meat markets, or blowing cigarette smoke at each other across empty warehouses in the early hours.

It was all about atmosphere, apparently…

But the truth was over-lit and dirty-white. It sounded like the hum of distant traffic and felt sticky against the soles of your shoes. It smelled of old blood or fresh bullshit, and no amount of gasometer-filled skylines was going to make it gritty. The atmosphere – in sweltering front rooms and shitty little offices – could make your guts jump for sure, and the hairs on the back of your neck stand to attention, but truthfully, it was rarely one of menace. Or of danger.

Watching people sob, and rant, and lie. Watching them tremble and gulp down grief.

It was more like embarrassment.

When he stepped off the bus, he looked pretty thrilled with himself; as though his journey home had been a riot of well-told jokes and stirring tales of sporting success. Yvonne Kitson was pleased to see that one look at who was waiting to meet him seemed to change the young man’s mood in an instant. Pissing on Adrian Farrell’s chips made her a very happy woman.

‘Good day at school, Adrian?’

Farrell looked straight through her. He ignored the shouts and the waves of friends banging on the windows of the bus as it moved off and passed him.

‘Did you have history today? I remember you said that was your favourite.’ Kitson was talking on the move now, walking quickly to catch up as Farrell marched through spiky blots of shadow, cast by the trees planted every twenty feet or so along the broad pavement. ‘Got anything planned for the weekend? After you’ve got your homework out of the way, obviously…’

Farrell slowed a little, but he kept on walking, hitched his grey regulation rucksack a little higher on his shoulder.

‘What sort of thing do you and your mates get up to on a Saturday night? My kids are still a bit younger than you, so I’ve really got no idea what goes on, except that I’ve got it all to look forward to. The taxi-service stuff, I mean.’ She was ten, twelve feet behind him. ‘Pub? Clubbing? What?’

Despite their pace, they were moving relatively slowly past a row of detached houses, many of them set back a long way from the road and some with gated drives. Kitson had to quicken her step to get the other side of a Jeep that reversed across the pavement without a great deal of attention.

‘That student who was kicked to death. Remember, I told you about him?’ Kitson said. ‘He was killed on a Saturday night. Saturday, October the seventeenth last year. I’m sure you can’t remember exactly what you were doing that night, but I bet you were enjoying yourself, whatever you were up to…’

Farrell didn’t stop dead, but he slowed to a standstill within a pace or two. He mumbled something as he turned, raised his arms and let them slap back down against his legs. It was a remarkably childish gesture of frustration and annoyance.

‘Good,’ Kitson said, as she drew close to him. ‘Not that I couldn’t have kept up with you all day long. Chasing after three kids keeps you pretty bloody fit.’

‘This is ridiculous,’ Farrell said. ‘I talk to someone about this boy in the year below me who’s gone missing. I answer a couple of questions. Next thing I know I’m getting hassled for no good reason.’

‘Nobody’s hassling you.’

‘Right. So nobody’s following me into the precinct in the lunch-hour? You’re not turning up outside my house after school, telling me about your kids?’

‘I’m not here to talk about my kids.’

‘Really?’

A jogger came past, his face twisted into a grimace, as though the song on the iPod he had strapped to his arm was particularly tuneless.

‘I just wondered if you’d remembered anything else about Amin Latif,’ Kitson said. ‘Perhaps something came back to you.’

Farrell’s expression was one Kitson knew well. He looked irritated, inconvenienced perhaps, as though he were being kept from some important TV show he really needed to watch. ‘In terms of what, exactly? Have I remembered which hymn we sang in assembly?’

‘Anything at all. Me talking to you about it might have helped you recall something that had slipped your mind.’

‘It might have been “To be a Pilgrim”.’

‘How long have you known Damien Herbert and Michael Nelson?’ The two boys Farrell had been with in the shopping precinct the day before.

‘Are we changing the subject?’

‘I didn’t think we were getting very far with the other one.’

‘A few months, I suppose.’

‘Six months?’

‘Did I know them on October 17th last year, you mean?’

‘That’s as good a date as any.’

Farrell nodded, understanding, and raised his eyes as though racking his brains. After a few seconds he snapped his fingers, grinned and pointed at Kitson. ‘I think it was “Immortal Invisible, God Only Wise”,’ he said. ‘I knew it would come to me.’

The urge to lay hands on him was getting harder and harder to ignore. Kitson pointed to the school crest, embroidered on the pocket of Farrell’s blazer. ‘What’s it say on the badge, Adrian? What’s the motto?’

‘I’m really shit at Latin,’ he said. ‘Sorry…’

She reached slowly into her bag, took out a piece of paper. ‘So, without wishing to labour the point, we’ve established that the name Amin Latif doesn’t really mean very much to you. Yes?’

‘Not a great deal, I’m sorry to say.’

‘What about Nabeel Khan?’

A shrug. ‘No. I don’t think so.’

‘That’s funny.’ Kitson unfolded the piece of paper, turned it the right way up. ‘Because he seems to know you. See?’

Farrell looked at the picture and the impatience suddenly gave way to panic, then genuine anger. He pulled the heavy bag from his shoulder, let it drop, and swung it back and forth in front of him. ‘I’m not sure what you think that proves.’

‘I’m not sure it proves anything,’ Kitson said. ‘I just thought your parents might like to put one in a frame. Pop it on the piano.’

‘I’m saying nothing more without a solicitor present.’

‘Fine. Come to the station with me and we can organise one.’

‘We already have one.’

For a second or two, Kitson wasn’t certain who ‘we’ were. She wondered if Farrell meant himself and his friends. Then she realised he was talking about his family. ‘Whatever you like,’ she said.

‘Are you arresting me?’

‘Do I need to?’

‘Definitely.’ A twitch at the edge of the mouth; an aborted smile. ‘If you want to talk to me again, I mean. I think that you aren’t arresting me because, whatever you’ve convinced yourself I’ve done – and you’ve given me some fairly major clues – you don’t have any evidence whatsoever to back your ideas up. None at all. I think you’re worried, with fairly good reason, that if you did arrest me, you’d only end up giving yourself unnecessary paperwork. That all you’d have caused by the end of it was huge inconvenience to other people, and a lot of professional embarrassment personally. Is that about right?’

Kitson said nothing.

‘This is lame.’ He jabbed a finger at the E-fit. ‘It’s borderline mental, if you want to know what I really think.’ If Farrell had lost his composure, it had been for only a few seconds; it never seemed to be any longer than that. ‘Come to mention it, have you ever shown me any identification? How do I know you’re who you say you are? You might be some kind of nutter.’