To throw Atherton off the scent, she made sure she had her mobile and wallet and keys, but took off her quilted jacket and lay it outside the central cave before she took the one to her right. If he didn’t know the caves, it might fool him into picking the wrong entrance.

It was cold inside the cave, especially without her jacket, but while the stone acted as a natural coolant, it also insulated the place from the worst of the cold. And the snow couldn’t penetrate here, no matter how hard the wind blew it. The walls were slimy, cool and moist to the touch, veined with minerals and crystals. It was getting darker with every step she took from the main entrance. Soon she was bending over to keep going, and as yet she had heard no signs of Atherton following her. He had seemed out of shape as he made his way up the hill, despite his sturdy build, and he was probably pausing to catch his breath and try to work out which way she had gone. At least, that was what she hoped.

Soon, Winsome knew, the ceiling would hang so low that it would look impossible to get under. A novice would turn around and go back. But Winsome had been through more than once, and she knew it was higher than it looked, even though you had to crawl on your belly for such a long way that it was easy to panic if you were the slightest bit claustrophobic. And if you panicked, you got stuck.

The trick, she remembered as she lay on her belly and slid forward into the clammy darkness, was to pretend that you were a snake and could squeeze through the narrowest of spaces. She cursed the few pounds she had put on since she had last been potholing and vowed to go to the gym regularly if she survived this ordeal, but even with her arse feeling much bigger than she could ever bear it to be, she managed.

She slithered along on her stomach, oblivious to the sharp bits of rock and quartz here and there that cut into her. At the worst moments, she felt as if she were being crushed by an almighty weight, the breath squeezed out of her. For a few seconds, about halfway along, she stopped. There was silence except for the wind and water dripping somewhere. Now the rock underneath her was wet. About an inch of water had accumulated in the passage, soaking through her blouse and jeans, chilling her to the bone.

When she turned a slight bend in the passage, she knew she was almost there, and soon the rock above her seemed to draw up, like a press after it had done its work. In no time she was on all fours, the jeans around her knees shredded to rags. She had grazed her elbows and they hurt like hell. But she was almost there. It was pitch black now, and she was far enough away from any possibility of the light being seen, that she finally risked taking out her mobile and using its light to show her the low entrance ahead. It was just a hole in the wall, really, but Winsome knew that it led to a ledge about forty feet from the bottom of the enormous cathedral-­like cavern so many intrepid visitors had oohed and aahed over. She bent forward and squeezed through. After about five feet, she found herself on the ledge, which was wide enough to sit comfortably on.

The light from her phone didn’t have the power to illuminate the full glory of the cavern, but it was better than total darkness. If Atherton did follow her, if he chose the right path and made it under the overhang, then she would hear him coming and have time to stand in wait against the wall by the edge of the entrance and use his momentum as he came through the hole in the wall to hurl him forward over the edge. Whether the forty-­foot drop would kill him, she had no idea. It would certainly incapacitate him, and there would be no way he would be able to climb back up and get at her.

Winsome turned off the phone to conserve battery power and huddled against the wall, shivering, arms locked around her drawn-­up knees. As her eyes grew used to the darkness, she could just make out the shapes of stalactites and stalagmites and sense the cathedral vastness of the space she was in. She would stay where she was until she was certain Atherton had given up, or her backup had arrived and caught him, then she would crawl and slither back out again, hoping to God the drifting snow hadn’t completely blocked the exit.

Now there was nothing to do but wait. Water dripped. The wind moaned and whistled through the interconnected passages and made a deep humming music in the chamber. She heard a loud cry followed by what she thought were curses, swearwords. Atherton. She couldn’t tell where they were coming from, but they froze her blood. Again she heard howls and curses echoing around the vast space, as if she were being hunted by a pack of hounds, and she hugged herself tighter and tighter until she almost turned into a ball.

BANKS AND Annie signed out one of the police four-­by-­fours from the car pool for their journey. Neither Banks’s Porsche nor Annie’s Astra would handle the present conditions well. It was tough going, and Banks gritted his teeth as he drove every inch of the snow-­swept roads out of town. Neither said a word. Banks didn’t even put any music on. He needed all the concentration he could muster for the driving.

Out on the main dale road, through Fortford, Helmthorpe and Swainshead, the conditions were much worse, as Banks had expected. It hadn’t yet got to the point where any stretches were completely impassable, but it sometimes felt close to that, and once Banks skidded on a drift and clipped the dry stone wall before regaining control of the steering. Annie held on to him. It was hard to see. The windscreen wipers couldn’t keep up with the volume of snow. The only piece of good fortune was that there was hardly anyone else out on the roads.

For a while after they turned off the main road, which branches toward Belderfell Pass to the left and the high Pennine moorland beyond the source of the river Swain to the right, Banks thought they might have to stop and continue on foot. But the drifting was patchy and for every deep and difficult stretch to plow through they would get a few hundred yards of relatively easy driving.

Eventually, taking much longer than he would have liked, Banks pulled up in the yard of High Point Farm, happy to see that two squad cars had somehow managed to beat him there. Even better, one of the officers said he had used his police radio to send out for a snow plow from Crowborough, the nearest village, about seven miles north. There were telegraph wires leading to the farmhouse, Banks noticed, so Welles/Atherton clearly had a landline.

Winsome’s Polo stood in the yard, half covered by snow. Without touching it, Banks glanced through the windows. No Winsome. No keys in the ignition, no signs of a struggle. The snow had covered up any tracks that might have been in the yard, except their own. There were no indications of where Winsome and Atherton might have gone.

One of the uniformed officers told him there was also a red pickup truck in one of the outbuildings. Its engine was cold, which meant Atherton had probably been at home when Winsome arrived. Banks pulled up the collar of his three-­quarter-­length overcoat and surveyed the scene. Snow had drifted up against the front door of the low-­roofed farmhouse and one side of the barn. He thought there was something odd about the place when he looked closely. “What are those?” he asked Annie. “Those pens on the side.”

“That’s not a barn,” said Annie. “At least, it probably was once, but it isn’t now. They’re called lairage. They’re used to keep the animals waiting for slaughter. It’s an abattoir, Alan, a private bloody abattoir.”

Banks hurried over to the building, with Annie not far behind. The front door stood open, and the long fluorescent lights shone on the inner workings of the small abattoir, the motorized rail running lengthways along the ceiling, the dangling hook with its bloody curve, the central trough, boilers and spray hoses for skinning. They stood just inside the doorway, wary of contaminating what might be a crime scene. Not to mention frightened of catching something. Whoever owned the place certainly had no interest in cleanliness and hygiene. It stank to high heaven and the floor was caked in shit and blood and worse. Banks almost gagged; Annie held her nose and breathed through her mouth. She pointed, and Banks saw an object on the floor, a bolt gun. They would leave it for the CSIs. At least Winsome wasn’t here, though she might have been, Banks thought. There could have been a struggle, and Atherton had dropped the bolt gun. But where were they now?