There were views across open fields on either side and the low bankings you could easily walk over. But half a mile further on, the scenery changed. The trail entered a rocky gorge with sheer faces of crumbling limestone. The rock had been hacked into sharp angles by the crude blasting methods of the railway builders. The bramble-covered slopes above them would be impossible to scramble up, and there were lots of places to hide among the tumbled rocks and deep crevices.

They were still some distance from the point where Jenny Weston had tackled the climb on to Ringham Moor. Ahead, there would be police tape and officers posted to prevent them approaching too near to the crime scene.

‘Aren’t we chasing hares?’ asked Cooper.

‘We have to go through the routine.’

‘We ought to be looking at Jenny’s life. Not where she was, but why she was here.’

‘It’s procedure.’

Up ahead was a tunnel, a black shadow across the trail. The glimpse of light and greenery at the far end only emphasized the blackness they had to walk through to reach it. As they entered, the ground underfoot became softer and carved into ruts by bike tyres. In the middle, the walls and roof were panelled with curved planks and buttressed with iron. Water ran steadily down the wooden sides and dripped from the roof. They had to watch for the gleam and flicker of it in the weak light to avoid the splashes.

‘You’re dealing with the earlier victim, aren’t you?’ said Cooper.

‘Yes, Maggie Crew.’

‘If it’s the same assailant, I suppose the main hope we’ve got is Crew herself. She’s the only witness.’

‘She’s crucial,’ said Fry. ‘If we’re ever going to get an identification, it will be from her.’

‘Only potentially crucial, I suppose.’

‘Why?’

‘She can’t remember anything. Isn’t that right?’

‘I don’t think it’s as simple as that,’ said Fry.

The tunnel had been driven through the rock face at the centre of the gorge, where pink gneiss showed through the limestone. Ferns clung in patches, and a silver birch had tried to colonize a high ledge. The only sounds were the dripping and their own footsteps, until a hissing roar began behind them. They turned to see a racing cyclist, his head down, his face invisible behind an aerodynamic helmet and wraparound shades. He was well past before they could stop him.

The original chunks of dressed stone in the tunnel walls had been filled in here and there with bricks. The number of small stones that had fallen at each side of the path looked a bit ominous, as if the tunnel was slowly crumbling around them. Behind the boarding, a mass of stone that had rolled down from the limestone face was prevented only by the damp boards and rusted iron from closing the trail completely.