'Some of my friends do,' said Liam. He laughed. 'Joke.'

Shepherd grabbed him by the back of the neck. 'Come on, let's go home.'

They climbed into the Honda CRV, Liam and the dog in the back, Katra and Shepherd in the front. When they got home Lady rushed into the garden and Liam hurried upstairs to shower. Katra began preparing vegetables while Shepherd made himself a cup of coffee. He carried his mug through to the sitting room and dropped down on one of the sofas. Liam's mobile was on the coffee-table and he picked it up. He looked through the Gallery at the videos Liam had taken of his attempts at dog-training and laughed as he watched Lady refuse to sit, confuse 'stay' with 'bark' and jump up to lick the lens at every opportunity.

Shepherd clicked on another video but his smile vanished when he saw what had been recorded. A boy of about Liam's age was being attacked by half a dozen teenagers. He was black, and howling as the larger boys kicked and punched him. The attackers were whooping like angry chimps and someone was filming the attack, urging them on. The video went on for a full ninety seconds and there was no let-up in the beating.

Shepherd sat back in his sofa and ran his hand over his face. It hadn't been horseplay: it had been a frenzied, vicious attack, and there was no doubt that the boy was hurt. He played the video again. The quality wasn't great but he could make out blood trickling from the victim's nose and hear the thuds of the kicks.

He sipped his coffee and played the video for a third time. The violence wasn't as shocking now, but it was still a horrific a.s.sault. Shepherd took the phone upstairs. Liam was in his bedroom. He'd showered and changed into a Pokemon T-shirt and blue jeans and was towelling his hair dry. He grinned when he saw Shepherd, but his face fell when he saw how angry he was. 'What's wrong?' asked Liam. Then he saw the phone in Shepherd's hand. 'What?' he repeated. 'What is it, Dad?'

'The video where did you get the video?'

'What video? What are you talking about?'

Shepherd held the screen towards Liam and pressed the b.u.t.ton to play the clip. When the video finished, he glared at his son. 'Well? What do you have to say for yourself?'

'What are you doing checking my phone?' protested Liam.

'Strictly speaking, as I pay the bill every month, it's my phone,' said Shepherd.

'You were spying on me!'

'I was looking at the videos we took of Lady, but that's not the point. The point isn't what I was doing, the point is how did that video get on your phone? Did you take it?'

'Of course not,' said Liam. He threw the towel onto the bed, picked up a comb and ran it through his hair. He turned his back on Shepherd so that he could look at his reflection in the dressing-table mirror.

'Liam, where did you get the video from?'

'Somebody Bluetoothed it to me.'

'Who?'

'A boy. At school.'

'Why?'

Liam sighed theatrically. 'Everyone was getting it. It's nothing. Just a happy-slapping video.'

'A what?'

'You know. Happy slapping. It's not serious.'

'Liam, a boy was a.s.saulted.' He sat on the bed. Liam finished combing his hair and turned around. 'Do you know who the boy is?' Liam shook his head. 'He was bleeding, Liam. He was hurt.'

'Dad, it's just a bit of fun. You see worse on TV all the time.'

Shepherd held up the phone. 'No. This isn't a clip of someone doing something stupid, this is an a.s.sault. A criminal a.s.sault.'

Liam bit his lower lip. 'I'm sorry.'

'I need you to promise me that you weren't there when the boy was a.s.saulted.'

'I wasn't, Dad. I swear.'

'Okay, I believe you,' said Shepherd.

Liam held out his hand. 'Can I have my phone back?'

'I'm going to need to hang on to it for a while.'

'Am I in trouble?'

'You're not in trouble, Liam. But next time someone offers to send you a video of someone being hurt, I hope you'll do the sensible thing and say no. Okay?'

Liam nodded solemnly. 'Okay.'

Shepherd was up bright and early on Sunday morning. Liam and Katra were still asleep when he left for his run. Lady was lying in her basket and she wagged her tail hopefully when he went into the kitchen. He patted her, then went to get his rucksack from under the stairs. He ran for the best part of ninety minutes, alternating between fast sprints and steady jogs, breaking midway for twenty minutes of sit-ups and press-ups. He was bathed in sweat when he got back to the house and helped himself to a plastic bottle of Evian water. He gulped it down greedily. A phone tree for Liam's cla.s.s was stuck to the fridge so that all parents could be contacted in the event of a school emergency. The name of the teacher, Miss Claire Tonkin, was at the top and the bottom. Liam's phone was where he'd left it on the kitchen table. He picked it up and tapped out Miss Tonkin's number. He half expected her to have switched the phone off because it was Sunday but it rang out.

'Miss Tonkin?' he said.

'Yes?' she said, her voice hesitant.

'I'm sorry to bother you on a Sunday. This is Dan Shepherd, Liam's father.'

'Oh, h.e.l.lo, Mr Shepherd Liam's okay, I hope?'

'He's fine, but there's something I'd like to talk to you about. I know it's Sunday but I have to go to London this evening and I won't be back until next weekend.'

'What's the problem, Mr Shepherd?'

'I think I'll have to show you, Miss Tonkin. But it's about a possible a.s.sault on a pupil. You'll understand when you see what I have.'

'This is very unusual, Mr Shepherd.'

'I know, but it is important and I can't see any other way of bringing this to the school's attention. I really do have to be in London tonight.'

The line went quiet. Shepherd paced around the kitchen. Lady whimpered and wagged her tail tentatively as if she sensed his unease. 'If it's that important, then I suppose you could come around to my house. But it'll have to be in the next hour or so I have to be somewhere for lunch.'

She gave him her address and ended the call. Shepherd went upstairs, showered and changed into jeans and a black wool sweater. By the time he went downstairs again, Katra was in the kitchen.

'I have to go out for a while,' he said, picking up Liam's phone. 'I'll have breakfast when I get back.'

He took the phone into the sitting room, removed its memory card and transferred the video of the boy being a.s.saulted from the card to a thumb-drive. Then he drove to Claire Tonkin's house, which was in a neat terrace on the outskirts of the town. Liam's teacher wasn't anything like he'd imagined her to be from the voice on the phone. He'd expected a fifty-something spinster in tweeds but she was in her late twenties with shoulder-length blonde hair and a disarming smile. While she wore a conservative dark blue dress and a white linen jacket there was no hiding the fact that she had a figure to turn heads. She had a strong, confident handshake and she looked him in the eye, then took him through to her living room. It was pleasant, feminine, with a comfortable three-piece suite arranged around a Victorian fireplace. There was no television, Shepherd noticed, but several shelves packed with books, most of them hardbacks. 'Please, sit down,' she said, waving to the sofa. 'I have to say it's a pleasure to finally meet you you seem to have missed most of the parentteacher evenings recently.'

Shepherd grimaced as he sat down. 'Actually, I've missed them all,' he said. 'I travel a lot for work.'

'You're a policeman, Liam tells me.'

'Sort of,' said Shepherd. 'I work for SOCA, the Serious Organised Crime Agency. We do investigative work but, strictly speaking, we're civil servants rather than police officers.'

'But you do get to arrest the bad guys?' she said.

Shepherd grinned. 'Occasionally.'

'That's good to hear,' she said. 'So, how can I help you? You said something about a pupil being a.s.saulted.'

Shepherd took Liam's mobile from his pocket. 'I found a disturbing video on his phone, a video of what looks like a boy being abused.' He saw a look of revulsion flash across her face and held up a hand to rea.s.sure her. 'Physically abused rather than s.e.xually,' he said. 'It's what they call "happy slapping". A group of boys. .h.i.tting another boy. But it's quite savage and the boy is obviously hurt.'

'The boys in the video are from our school?' asked Miss Tonkin.

'Liam doesn't know. He says he doesn't recognise anyone in the video. It might not even be the school here, of course, but I wanted to check with you. Even if it happened somewhere else it still needs investigating.'

'So Liam didn't film the attack?'

'Good Lord, no,' said Shepherd. 'A boy in his school Bluetoothed it to him a couple of days ago.'

Miss Tonkin held out her hand. 'May I?' she asked.

'Sure,' said Shepherd. He called up the video and showed her how to start it. She watched it with a growing look of horror on her face. 'This is awful,' she said, when the video had finished. 'Absolutely awful.'

'Do you recognise the boy?'

'I'm afraid I don't,' she said, 'but it's a big school.'

'Has a pupil been injured recently?'

She frowned. 'I don't think so.'

'It's hard to see on the video just how hurt the lad is,' said Shepherd. 'The resolution isn't great but it looks as if he's bleeding and there's a good chance that he'd have been taken to A and E. That's not rough-and-tumble, it was a real beating.'

Miss Tonkin nodded. 'You're absolutely right,' she said. She watched the video again. When it had finished, she shook her head. 'Terrible.' She held up the phone. 'Can I keep this?'

'I've made you a copy,' said Shepherd, handing her the thumb-drive. She pa.s.sed him back the phone. 'What will you do?' he asked.

'I'll try to find out who the boy is, obviously. Then we'll take it from there. We have zero tolerance to bullying, I can tell you that much.' She smiled. 'I do appreciate you bringing this to my attention, Mr Shepherd.' She stood up and extended her hand. 'Rest a.s.sured, I'll deal with it. And I hope it won't be too long before we see you here again. At the parentteacher evening next month, perhaps?'

'I'll do my best,' said Shepherd. He couldn't help thinking that if he had known how attractive Liam's teacher was he would probably have made more of an effort to attend PTA events in the past. She showed him to the front door.

When Shepherd got back to the house, Liam was in the kitchen eating cheesy scrambled eggs. Shepherd sat down at the table and gave him his phone back. 'I went to see Miss Tonkin,' he said.

Liam put down his fork. 'You did not,' he said. 'Why, Dad?' He put his head into his hands.

'She has to find out what happened to the boy in the video,' said Shepherd. 'He was hurt, Liam.'

'But, Dad, everyone will think it was me that gave it to her.'

'No, they won't. And if they do, just tell them it was your dad. Someone has to investigate what happened that boy could have been seriously hurt.'

Katra put a mug of coffee in front of Shepherd. 'What do you want for breakfast, Dan?'

Shepherd gestured at his son's plate. 'I'll have what he's having. With toast.'

'Dad, am I going to be in trouble? Because of the video?'

'You weren't involved in beating up the boy, were you?'

Liam shook his head.

'And you weren't there when it happened?'

'I just got the video, Dad. I swear. I told you yesterday.'

Shepherd smiled. 'Then everything'll be fine,' he said. 'You didn't do anything wrong.'

'But I don't understand why you had to talk to Miss Tonkin.'

'Because that boy was hurt,' said Shepherd. 'It wasn't horseplay, it was a savage beating. You're sure sure you don't know him?' you don't know him?'

Liam shook his head. 'It was just a funny video, that's all. Like you see on TV.'

'Well, next time I hope you'll realise that it isn't funny when someone gets hurt,' said Shepherd.

Shepherd got back to London late on Sunday night. First thing Monday morning he took the Tube to Paddington Green, picked up his leathers and motorcycle helmet and went along to collect his bike from the Hyde Park car park. As he drove it back to the police station, he felt his phone vibrate to let him know he'd received a text message. He showed his warrant card to the guard at the entrance to the police car park and, after the man had checked a list on a clipboard, the metal gate rattled up and he drove in.

After he'd parked next to two Traffic bikes, he took out his phone. The message was from Martin O'Brien. 'All sorted. Ready when you are.' Shepherd smiled and put the phone back in his pocket.

There were two CCTV cameras covering the level he was on, one pointing at the exit, another in a corner giving a general view of the parking s.p.a.ces. He took off his helmet and walked slowly towards the TSG's vans. He put his right hand into his jacket and took out one of the transponders Singh had given him.

The vans used by his Serial were the seventh, eighth and ninth in the line. He glanced over his shoulder, checking the position of the CCTV camera behind him. When he reached the first van he moved to the right and bent down as he reached the offside rear wheel arch. He pressed the b.u.t.ton at the end of the transponder and the green light winked on. He slipped the transponder under the wheel arch and felt it fasten itself under the rim. He straightened up and walked around the rear of the van, close to the wall. He stopped and listened but there was n.o.body else in the parking area. He took the second transponder from his jacket pocket, switched it on, and walked behind the next van. He slid the transponder under the rear nearside wheel arch and felt it click into place.

He took out the last transponder as he walked to the third van. Once he had slotted it under the wheel arch, he went to the locker room, swinging his helmet.

While he was changing into his uniform, Nick c.o.ker and Barry Kelly arrived. 'You're in early, Terry,' said c.o.ker.

Shepherd looked at his watch. There were fifteen minutes to go before his shift started. He'd wanted to get in early to attach the transponders. 'Yeah, traffic was light.'

'Didn't think traffic worried you h.e.l.l's Angels,' said Kelly. 'And you can use bus lanes now, right?'

'Wouldn't catch me on a bike,' said c.o.ker. 'Half the drivers in London don't have a licence.'

'That's a fact, is it?' asked Shepherd, taking off his polo shirt and hanging it in his locker.

'You should talk to Traffic,' said c.o.ker. 'It's a b.l.o.o.d.y nightmare out there. You think the illegals bother with licences never mind tax, insurance and MOT?'

'I guess not,' said Shepherd, taking his police shirt from the locker.

'd.a.m.n right,' said c.o.ker. 'If one of them knocks you off your Harley he won't be hanging around, that's for sure. Off like the b.l.o.o.d.y wind.'