As one armed officer yanked open the left-hand barn door, Tony Lennis, breathing apparatus on, moved swiftly inside, his Heckler and Koch MP5 submachine gun held out in front of him, followed immediately by two of his most experienced officers. Although the lights had been turned off on the ground floor, powerful spotlights from outside were shining through the two narrow windows at the front, illuminating the smoky interior enough for Lennis to spot the corpse of a tall skinny guy in the middle of the stone floor. He had intelligence that there might be a twenty-nine-year-old IC1 female being held captive somewhere in here, but he couldn't see her and had little desire to go upstairs where the fire had clearly been started, in case he got trapped.

A bullet hissed past his head, and one of his people – Jim Walton, a recently divorced father of three kids under ten – went down with a muffled yelp. Another round flew past, narrowly missing Lennis again, and he realized that in twenty years of armed service this was the first time he'd ever been fired at with live ammunition; and worse still, whoever was firing was good.

The shots were coming from behind a partly open door straight ahead, but neither the assailant nor his gun was visible.

To his credit, Lennis didn't hesitate. Nor did his other colleague, recently married Terry 'One Shot' Landesman. They both opened up with the MP5s, the bullets knocking open the door with a loud crack.

A shadow moved beyond it and Lennis let off another burst of fire, the torch beam from his MP5 lighting up the gloom. Where the fuck was he?

'Officer down!' he shouted into his mouthpiece as more officers poured in through the barn door. 'Repeat, officer down! We need urgent medical assistance!'

Lennis knew he had very little time. Ordinarily he would have secured the ground floor then waited while his superiors attempted further negotiation, but the fire was spreading fast above them and it wouldn't be much longer before the wooden ceiling gave way, condemning them all to a fiery grave.

With his heart hammering in his chest, he advanced on the open door, Landesman by his side. Lennis went through first, pointing his weapon up the wooden staircase that led to the next floor. The smoke was everywhere here and he could hardly see a thing.

Then another bullet hit the wall just behind him, and he returned fire, the sound of the discharge making his ears ring.

A shadow flitted across the balcony and Lennis fired again, moving his weapon in a tight arc, his rounds tearing up the woodwork. He thought he heard a scream and saw a figure stumble as if he'd been hit, but visibility could be measured in feet and it was impossible to tell for sure. He became aware of Canaver calling out on the megaphone for the man to surrender, but his voice was stifled by the crackle of the fire and the sound of his own breathing.

With a nod to Landesman, he raced up the stairs, eager to press his advantage, operating on instinct now, not thinking of the dangers inherent in his actions. As he reached the top, the smoke seemed to swallow him up, and he felt the heat of the fire against his protective overalls. He turned the corner, finger tensed on the MP5's trigger, and almost tripped over the body of the gunman at his feet. He'd been shot in the head, the pistol with silencer still in his hand. It was hard to tell whether he was dead or not, but he was definitely in a bad way.

But it was the sight of the girl in handcuffs lying on the floor a few feet away through an open door that grabbed Lennis's attention. Her face was smoke-blackened and she was choking beneath her gag, eyes tight shut in an effort to keep out the smoke.

Lennis ran forward, ignoring the heat from the flames as it came at him in intense waves, and heaved her up from the floor. Then, helped by Terry Landesman, who took one of her arms, they hauled her from the room.

'What about him?' asked Landesman through his mouthpiece, nodding towards the gunman.

'Leave him,' panted Lennis, knowing they had only moments to get out. 'He's not worth risking our necks for.'

As they helped the girl down the staircase, a loud crack rang out from the ceiling above the main barn, and Lennis saw a long, twisting split appear right across it. He knew it was going to give any second and he was tempted to drop the girl and make a dash for it, but he knew without a doubt that he'd never be able to live with himself if he did that. Instead, he stopped and heaved her over his shoulder.

'Go on, go!' he snapped at Landesman, and the two men made a dash across the floor as another crack sounded above them and the ceiling began to buckle. 'It's going!' he shouted through the mouthpiece as he charged out the door and across the track before falling to his knees and setting the barely conscious girl as gently as he could on the grass as the paramedics moved in.

Behind him there was an almighty crash as the ceiling finally collapsed, interring the gunman in a fiery grave. Lennis felt a sudden surge of euphoria. He'd made it.

Thick black plumes of smoke continued to pour from the badly damaged barn while more than a dozen police and TV helicopters flew slowly in a wide circle overhead vying for the best view of the dramatic scene that was being played out over the few square miles of countryside below.

A three-mile exclusion zone had now been set up around the burnt-out gas lorry, and a major evacuation of the area's residents was already underway, although the effects of the phosgene had been severely limited by the rain that was still falling, coupled with the lack of a strong wind. So far the only confirmed casualties were the lorry's driver, who'd been incinerated in the blast, and his passenger, who'd been rushed to hospital suffering from the gas's effects and who was not expected to live.

The barn lay just a few hundred yards outside the exclusion zone, and three separate fire crews were still working to bring the blaze under control. Further back, behind the police lines, Mike Bolt and Mo Khan, both of them exhausted, stood watching them alongside the police and ambulance crews. Big Barry Freud had arrived by helicopter a short while earlier and was now in the process of taking charge of the crime scene from his colleagues in Essex on behalf of Counter Terrorism Command.

Bolt, still hyped up by his recent experiences, was drinking a hot mug of coffee, while Mo was smoking a sneaky cigarette, having fallen off the non-nicotine wagon once again. When Bolt had given him a disapproving look, Mo had answered simply, 'It's the stress of working with you,' and Bolt could hardly disagree. Neither had said much to the other since their narrow escape from the bomb nearly an hour earlier. They were both still getting over the shock of it, and Bolt knew that there was no way either of them was going to be sleeping much tonight.

Tina, meanwhile, had been transferred to hospital, where she was now being treated for her injuries. She'd drifted in and out of consciousness in the immediate aftermath of the explosion so Bolt hadn't been able to ascertain what had happened to her during the thirty or so hours she'd been missing, but the word from the hospital was that she was going to be OK, and he was looking forward to visiting her there as soon as he could.

In the end, things had worked out as well as they could have done. The mustard gas lorry had been intercepted; a woman believed to be Jenny Brakspear had been rescued alive from the burning building by one of the armed response officers; and it seemed that Hook had never made it out, and was therefore almost certainly dead. Bolt was pleased: someone like him didn't deserve the comparative luxury of a British prison. But he would have liked to look into his eyes while he died and say, 'This is for Leticia Jones, you callous bastard.' Bolt knew that some people would say acting like that made him almost as bad as Hook, and he could see their point. Ordinarily he didn't believe in the death penalty, yet there were people out there – not many, but some – who were so corrupt, so depraved, and most important of all so dangerous that it was more of a crime to let them live. Hook was just such a man, and when the time came, Bolt would raise a glass to his passing.