Up ahead, the lights at the Gloucester Place junction were green and Obanje and the suspect bike went through them fifteen yards apart, while Bolt, fifty yards back and driving like a maniac, with the siren blaring, was beginning to lose visual.

The lights turned amber, and a Ford Focus twenty yards in front of Bolt stopped.

'Hold tight!' he yelled as he slammed his hand hard down on the horn and accelerated straight at the back of the Focus, hoping it would get the message quickly.

It did, but just a little bit too late. It was still only halfway out of the lane when Bolt smacked its offside rear end and shunted it out of the way without losing speed.

'I take it all back,' he said to Mo as they tore across the empty junction. 'I love this car!'

'Bike one to all units, he's approaching Baker Street junction, traffic lights have just turned red. He's going right! He's going right!'

'Keep with him!' snapped Bolt, mounting the kerb on the central reservation as he forced his way past some slow-moving traffic.

'I'm through. We're heading south on Baker Street. All right, he's going left. Left. I think it's Paddington Street. Shit!' This last word was a shocked howl.

'Car one to bike one, what's happening?'

'He's firing at me!'

There was the sound of a skid, followed by a loud grunt, then the engine noise abruptly stopped.

Bolt accelerated with two wheels still on the central reservation, taking off wing mirrors and the side panelling of a Range Rover as he bore down on the Baker Street junction. 'Bike one, are you OK?' he shouted into the mike.

'I'm OK,' came Obanje's voice. He sounded winded. 'But I'm down. Suspect continuing along Paddington Street east. Christ!'

'What's happening?'

'He's been hit by a car. He's down. About a hundred yards away. Getting to his feet now. But he's hurt. Repeat: he's hurt.'

The lights at the junction were red, but Bolt knocked the last car out of the way, slowed a little as he moved out into the oncoming traffic, which thankfully stopped for him, then roared off down Baker Street. 'Car one to all units, I'm right behind.'

'Bike one to all units. Suspect has crossed the road, heading south, disappeared from view into what looks like a park. I'm following but unarmed and hurt. Over.'

Bolt saw Obanje hobbling along the pavement in his leathers, helmet off, as he rounded the turn into Paddington Street. Obanje pointed along the road, and with the traffic now clear Bolt put his foot down, almost immediately spotting a small stretch of greenery on the right between high-rise buildings.

Screeching to a halt, he pulled out the Smith and Wesson, Mo following suit, although with considerable reluctance, Bolt noticed.

'Stay here,' he told Tina, then jumped out of the car and ran through the park entrance, holding his gun in both hands, Mo just behind him.

He saw Hook immediately, fifty yards ahead, limping along the path with his back to them, the helmet now removed, his gun nowhere to be seen. The day was cloudy and the park fairly quiet, but there were still enough people about to make it an incredibly dangerous situation should the bullets start flying.

Bolt ran fast and as quietly as possible, whispering the suspect's location into the mike, hoping Hook didn't hear his approach, knowing that if he got close enough and the other man turned round he might be able to shoot him justifiably. With the way public opinion was reacting to this latest terrorist outrage he knew he could get away with it. What was worse, he desperately wanted to do it. A small voice in his head urged calm and restraint, told him to remember what he'd joined the police for. But it really was a small voice, and at that moment the desire for payback was smothering it almost completely.

A woman walking her dog across the grass saw the gun in Bolt's hands and screamed, the sound carrying right across the park.

The limping figure immediately turned round, and even though he was still some thirty yards distant, Bolt recognized him. He raised his gun, still too far away to risk pulling the trigger. 'Armed police!' he yelled. 'Raise your hands!'

Hook ignored him, making for the far end of the park, trying hard to run but not quite managing it. At the same time he pulled what looked like a handgun from his jacket, although he made no effort to fire it, clearly knowing that Bolt couldn't shoot him in the back.

A woman with a pushchair and a young child walking beside her was coming the other way, and before she could react, let alone comprehend what was happening, Hook had grabbed the child and swung back round to face his pursuers.

The child, no more than three years old, cried out, and Bolt instinctively lowered the gun, not wanting to risk it going off accidentally.

Immediately, Hook lifted his and fired straight at Bolt, who dived to the ground, rolling over but keeping his grip on the gun, scrambling for cover behind a sapling while Mo did the same behind a bench opposite. A second shot rang out, but handguns are notoriously inaccurate over distance, and it too went wide. People were running in all directions now as Bolt shouted the latest developments into the mike.

The child's mother made a grab for Hook, crying hysterically, and Bolt jumped to his feet, seeing an opportunity to intervene. But before he'd even taken a step forward, Hook had pushed her away and shot her in the chest.

For a split second, Bolt was too shocked to move.

Then, with a roar of frustrated rage, he charged his quarry.

But Hook stood his ground and pulled the trigger again.

Bolt stumbled and fell forward on to the path, and this time the gun flew out of his hand. For a second he thought he'd been hit, but then he realized that his fall had been an instinctive reaction to the gunshot and that once again Hook had missed.

Hook threw the child away like a piece of rubbish, and as Bolt got to his feet again he saw him hobbling out of the park's exit.

The bastard was going to get away. Where the hell were the reinforcements? A helicopter? Anything?

As he grabbed his gun and ran towards the mother, who lay writhing on the grass – still alive, thank God, her child unharmed – he yelled his frustrations into his mike, demanding paramedics and back-up in a flurry of expletives. If Hook got away now it would be a travesty of everything he, Bolt, had ever fought to defend. It would make every good deed he'd done seem utterly pointless.

He sprinted for the exit, shouting at Mo to stay with the injured woman, knowing he'd pull the trigger the second he had Hook in his sights.

And then he heard the sound of a vehicle coming from beyond the fence bordering the park, followed by a tremendous metallic crash.

Tina heard Bolt's breathless commentary on the mike in the back of the Shogun. Then she heard the shots, and she knew she couldn't just do nothing. She had to be involved. Had to do something to bring the man who'd shot her and murdered an innocent woman in front of her to justice, especially now it sounded like he might be getting away.

The keys to the Shogun were still in the ignition, and she clambered out of the back door and got in the driver's side, easing herself slowly into the seat. Thank God it's an automatic, she thought as she placed the car in drive and put her good foot on the accelerator, driving out into the traffic and turning first right to circumnavigate the park.

She had no real plan as such, and the painkillers she was full of were making her drowsy, but if she could just get a visual on the animal Bolt had told her was called Hook, that would be enough. She wanted to see him arrested. Or, better still, look down on his dead body.

Bolt's voice filled the car again. 'He's exited the park south-east side! I've lost the visual and we've got a casualty!'