With only one door to get through, as opposed to a pair of them coming at the property from the front, the rear entrance was favourite. More importantly, when firearms were being deployed, keeping the action well away from the street was always desirable.

Thorne didn’t blink.

For twenty, twenty-five seconds, the image was constant, then suddenly it filled with movement as a dozen or more figures began crowding in. Moving into the picture from the back and sides of a scrubby, unloved garden; over and along the line of a crumbling wall towards the bottom of the steps.

Then a flurry of hand signals, and up; speed less important than stealth.

The team gathered around the door, and Thorne picked out what details he could, imagining those that were too indistinct to make out: the butt of an MP5 carbine; the MET POLICE logo on a chest thick with body armour; the dead geraniums in a plastic window-box…

In the van, a few murmured instructions came over the speaker.

Thorne could make out Porter and Parsons, and several heads he thought he recognised. He watched two figures move into the picture and knew – though he couldn’t see it – that they would be fixing the rubberised teeth of a hydraulic jack to either side of the door frame. These were members of the Special Events team – the Ghostbusters – a civilian unit on call to any branch of the Met that needed to gain rapid entry to premises but wanted something rather more subtle than a ram or a size-nine boot.

The SE boys stepped away from the door, trailed the cables back to a small generator and signalled that they were set.

They looked towards Porter for the nod.

Got it straight away.

There was no sound from the monitor, but Thorne had worked with similar forced-entry equipment before. He imagined the sharp hiss of compressed air and the slap of the cables jumping against the metal floor. The crack as the frame was shunted wide, leaving the door with nowhere to go but in and down, forced hard to the floor by the feet of the SO19 officers who streamed across it into Conrad Allen’s flat.

In a matter of seconds the shot was empty again, a flat shadow beyond the doorway, while its chaotic soundtrack was broadcast from half a dozen radios, exploding like bursts of gunfire from the speaker. Bouncing between the metal walls of the van: a collision and a curse; an order given to get out of the way; and an instruction to anyone on the premises to make themselves fucking visible very fucking quickly. A cacophany of grunts and shouts:

‘Kitchen clear!’

‘Armed police!’

‘First bedroom and corridor clear.’

Thorne winced at each distorted spatter of voices and volley of breath, focused through every crackle of static. He pictured the officers running, freezing, pressing themselves against walls; sweeping the space through rifle-sights, moving sharply aside as other figures passed through shadows, barrelled in and out of rooms.

‘Clear!’

‘Clear and secure!’

Heeney muttered at Thorne’s shoulder: ‘The place is empty.’

‘Shut up,’ Thorne said.

A shout then, audible above the others. Just one word. Just the crucial word.

‘Body.’

‘Say again?’

‘We’ve got a body.’

Thorne stands up, crouches, pushes his hands against the roof. He strains to hear more, to hear anything through the hiss, through elastic seconds of dead air.

‘Where?’

‘In here.’

‘Where the fuck’s “here”?’

‘Back bedroom.’

And Thorne can see it when he closes his eyes. He’s seen it before, or close enough: the sole of a training shoe, a mop of dark hair, a great deal of blood.

‘Jesus,’ Heeney whispers behind him, but Thorne is already moving towards the doors, putting a shoulder against them, and tearing across the road in the same direction Porter had gone just a few minutes before.

Pain blooming in his back and chest as he runs, and more pictures he could do without: fingers and thumbs, grubby on the barrel of a syringe; the tremble around Juliet Mullen’s mouth.

A pair of armed response vehicles, three squad cars and an ambulance are already parked up on the track that runs along the back of the building, and the garden is thick with the Job by the time Thorne drops on to the other side of the low wall. Body armour is laid down, sweaty on the grass; stepped across by scene-of-crime officers, scrambling into full-body suits and hurrying towards the fire escape. There is conversation and clatter as a constant stream of Met personnel shuttle up and down the metal staircase. A necklace of cigarette smoke curling past them towards a clear sky, and Holland at the bottom, turning to Thorne, his arms raised, asking:

What the fuck’s going on?

‘Tom…’

Thorne spun round and saw Porter moving towards him across the grass. Breathless and none too polite, he asked Holland’s unspoken question for him, then asked another before she’d had a chance to answer the first.

‘What about Luke?’

Porter shook her head.

‘Alive? Dead? What?’

‘We’ve got two bodies up there,’ Porter said. ‘Almost certainly those of Conrad Allen and his girlfriend. Both look like they’ve had their throats cut; to start with, at any rate. There’s a knife.’

‘So where’s the boy?’ Thorne asked.

In a hurry, or sick of being barked at, Porter turned and started to walk back towards the cluster of vehicles. She answered without bothering to look round. ‘Right now it’s impossible to say, and I can’t see any point in speculating. I do know we’ve got a pair of dead kidnappers and a hostage who’s nowhere to be found.’

Before, when he’d woken up, when he’d come out of it, it had been horribly slow. Like surfacing through water thick as glass. Seeing what was on the other side, but without the strength to kick hard and reach it quickly. But this time, when everything had happened, it was as though he were conscious in a second, and as soon as he’d opened his eyes he’d been alert and alive to every sound and sensation.

He’d felt his blood jumping.

He’d heard the shouting immediately; the grunting and the noise of things smashing in the next room. They were arguing. He’d heard them fighting before, a couple of times, but this sounded really serious, and he guessed it was what had woken him so suddenly. Something inside his brain, some weird survival instinct that never switched itself off, had roused him, was telling him that this might be his chance.

As usual, when he’d first opened his eyes, he’d had no idea whether it was day or night. The curtains had been drawn tight across. But for almost the first time he’d been alone, with his hands untied, so after a minute or two he’d got up from the mattress on the floor, crept over and pulled the curtains back an inch or two. It was dark outside, but in the tower blocks opposite he could see lights in some of the windows and the flickering of TV sets. He’d guessed that it was probably early evening.

Trying not to breathe, he’d stood very still in the middle of the room, listening to the screaming from down the corridor.

He’d mentally mapped out the whole place during those first few trips to the bathroom. It wasn’t a complicated layout and he’d always been good at picturing stuff, at laying out diagrams on his computer and seeing how things connected. He’d known, standing there in the dark, that were he to take a left turn out of the room he was in, he would need to get through two doors before he was on the street. He knew that because he’d tried to run through one of them on the first day, which was when they’d started giving him the injections more often. Turning right would have been a better bet, but he knew that he would have had to go past their room, would have had to risk being seen, and he knew that there would still be a locked door between him and the back way out. He was fairly certain there was a way down through the kitchen: an old-fashioned fire escape like his nan used to have. He’d been almost completely out of it, but he could remember seeing the metal steps, hearing the man’s feet ringing against them as they’d carried him in.