‘That was Simon’s fault,’ Nicklin said.

‘Selfish of him,’ Thorne said.

They were twenty feet or thereabouts from the edge, though the drop was nothing like as steep as it was from the cliffs on the mountainous side of the island. It would not have been an altogether easy descent, but it would probably have taken no more than fifteen minutes to clamber down to an uninviting shoreline festooned with enormous, weed-covered rocks. No decent-sized boat could have reached the shore safely, certainly not at night, but that had not been Nicklin’s plan all those years ago.

Thorne watched him now, sniffing the air like an animal, and imagined the seventeen-year-old climbing down to the sea, having just buried Simon Milner; wading into the freezing water towards the boat that was waiting in the dark, the light from an accomplice’s torch.

‘Here,’ Nicklin said.

‘Sure?’

‘This feels right.’

Thorne looked across at Bethan Howell. ‘On you go…’

With fingers firmly crossed that the job would be finished before darkness fell, they had left the portable generator back at the school and carried the rest of the equipment down between them. Now, the various cases were laid down and opened up. Thorne saw straight away that the forensic team had brought along rather more than he had first imagined: hand trowels, buckets, sieves, tape measures, positioning rods, digital cameras and video recorders. A canvas bag held all the personal protection gear – scene of crime suits, nitrile gloves, elbow and knee pads, duct tape for sealing cuffs – while a smaller aluminium case that Howell had been carrying contained the ground-penetrating radar and computer equipment.

While the gear that was needed for the search phase was assembled, Howell led Thorne to one side. She kept her eyes on Nicklin, who was watching the preparations with considerable interest. ‘How do you want to do this?’ she asked.

Thorne looked at Nicklin too. ‘As soon as you’ve identified an area where you think it’s worth digging, I’m taking our friend back up to base. I don’t want him here for that.’

Howell nodded, getting it. ‘It’s the bit he’s going to enjoy.’

‘Watching us digging in the wrong place.’

‘You think he’s going to dick us about?’

‘Every chance,’ Thorne said. ‘And I’m not pandering to him any more than we have to. If it turns out to be what we’re looking for, then we don’t need him any more anyway and I’m getting him off this island first chance I get. I want him back in a cell as soon as possible.’

‘All makes sense,’ Howell said. She looked at Batchelor. ‘Why’s the other one here? Is he connected to the victim we’re looking for?’

‘Nothing to do with any of it,’ Thorne said. ‘Just Nicklin pulling our strings again.’

Howell and Barber went to work with plastic rods and twine, dividing up an area roughly twenty-five feet in either direction from the spot Nicklin had indicated, laying out a grid. Once that had been done, Barber began putting the GPR kit together; assembling long metal handles, firing up a laptop.

Howell laid a large geological map of the island on the grass and weighed down the corners with stones. This was the flattest, most exposed part of the island and the wind was really starting to bite. ‘We’ll do what we can,’ she said. ‘But this isn’t going to be quick.’ She clocked Thorne’s reaction, pulled a face of her own. ‘Listen, we’re doing it on the hurry-up as it is. If I had the time to do things properly I’d want to test core soil samples, but we don’t have the equipment here and sending it back to the mainland is going to take forty-eight hours minimum.’

‘I was hoping we could just pick a place to look,’ Thorne said. ‘Then dig until we find a body. I know that might sound like a bit of a simplistic approach…’

‘Simplistic is the only approach we’ve got,’ Howell said. ‘So far, this is all about what we can’t do.’

‘What can’t we do?’

‘We can’t use dogs and there’s no point using penetrometers.’ Thorne’s attempt at a confident nod of understanding was clearly less than convincing, but Howell seemed happy enough to reel off a paragraph or two of Forensic Archaeology for Idiots. ‘OK, we need to identify the areas where soil has been disturbed, right?’

Thorne nodded again, with it so far.

‘We could normally do that by measuring penetration resistance, because obviously soil is weakened when it’s already been dug up for a grave. All a waste of time when you’re talking about farmland.’

Thorne looked at her.

‘How many times do you think this field’s been ploughed in the last twenty-five years?’

‘Right, yeah.’

‘There’s also no point using the naked eye to look for anomalies… patches of richer vegetation, whatever. A decomposing body can release nutrients which work like fertiliser basically, so you’re just keeping an eye out for grass that’s lusher, darker. Again, no good to us, because this is animal pasture.’ She nodded towards a muddy ewe that was eyeing them nervously. ‘Because sheep-shit will do much the same thing.’ She raised a hand to acknowledge the wave from Barber, who was letting her know that they were ready to go. ‘So, as things stand, the GPR is probably our only option…’

It looked like a high-tech hand trolley; a metal box at the end of twin handles, fixed onto rubber wheels. Cables ran from the main GPR unit to a small laptop mounted at the end of the handle. Thorne looked at the picture on the small screen; a series of jagged lines against a grey background.

Howell pointed to the image. ‘That’s the plough layer, see?’

Thorne shrugged, seeing only squiggles.

‘So then there’s a smoother layer beneath that and we’re looking for evidence of disturbance that falls outside the expected parameters.’ She smiled at him. ‘Basically, we’re looking for something grave-shaped.’

It was already eleven thirty by the time Howell began a systematic analysis of each quadrant using the GPR. It was painstaking and frustrating to watch, the process not made any more enjoyable for anybody by Nicklin’s running commentary.

‘Not exactly a spectacle this, is it?

‘If you find buried treasure, do we all get to share it?

‘Shame about the cadaver dogs.’ He spoke the word with considerable relish. ‘Can they actually still smell a body after all this time? Amazing creatures, dogs… even if they do spend most of their time licking other dogs’ arses.’

He talked almost non-stop, his incessant jabber only highlighting the fact that Batchelor had been as good as mute since they’d boarded the boat almost four hours before. Each time a quadrant was ruled out and Howell and Barber moved into the adjacent section, Nicklin was quick to loudly express his disappointment.

‘I really thought this was the one.

‘I know it’s ages ago, but I was sure that was it.

‘I definitely remember looking back from somewhere round here, looking back at the lights in the farmhouse, just before I heaved him into the hole…’

They broke for sandwiches after an hour, a tray brought down to them by Robert Burnham’s wife. A few minutes into the first quadrant after lunch, Howell beckoned Thorne across. He stepped carefully over the lines of twine and, as soon as he had reached her, Howell pointed to the screen. The zig-zags made no more sense than they had the first time he had looked, but Thorne could see that Howell was excited.

‘Worth digging, you reckon?’

‘I reckon.’

‘Right…’

‘This is exciting,’ Nicklin said. He looked at Thorne. ‘Are you excited, Tom? You don’t look very excited.’

Thorne told Holland that he would be escorting the prisoners back up to the school and to stay in touch. Holland agreed to radio in every fifteen minutes and walked across to join Sam Karim and Wendy Markham, who had turned away from the wind, trying to stay warm. Markham had been carefully watching the forensic team at work, not least because – though it was far from riveting – focusing on the job had allowed her to short-circuit several unpromising conversations with Karim. Now, the exhibits officer shouted across at Thorne as he and the party from Long Lartin began trudging uphill towards the track.