Fry sighed. ‘Have we got a map or anything?’ she said.

They knew that Jenny Weston had set off from Partridge Cross an hour and a quarter before her death. She had headed eastwards on the High Peak Trail, where the strip of black compacted gravel provided easy going. Beech and elder trees overhung the trail, with nettles and brambles dying back on the verges. Jenny would have passed under the A515 before she left the trail and crossed the route of the old Roman road to begin the ascent to Ringham Moor.

The mist began to break up as they climbed away from the hire centre. A jet liner went overhead towards East Midlands Airport, leaving a white streak in the sky. A farm dog barked half-heartedly in the distance. In between the noises, it was so unnaturally quiet that when a flock of pigeons passed overhead the noise of their wings sounded as loud as the jet.

But a few people were already starting to arrive on the trail. A woman with iron grey hair jogged by. She was wearing purple Lycra and a clashing yellow bum-bag, and she had two large, shaggy dogs panting to keep up with her. Cooper stopped her and ran through the questions on his list. Had she been this way yesterday afternoon? Did she remember seeing this cyclist? He showed her the snapshot of Jenny Weston provided by her father, and described her bike and clothing. If not, who else had she seen? The woman did her best, but couldn’t help. She urged the dogs on as she crunched away again.

Walkers began to appear in pairs, and once there was a small group of half a dozen. They all said ‘hello’ to the detectives, even before they were asked to stop and answer questions.

‘Is it obvious who we are?’ asked Fry uneasily.

‘No, it’s just the thing to do, if you’re walking out here. It’s a sign of comradeship.’

Fry snorted. Then a lone man passed them, walking slowly, with his head down. He was wearing a worn anorak, and his hair was dark and greasy. Fry’s eyes hardened and her shoulders tensed. The man glanced at them nervously as he passed.

‘Morning,’ he said.

Cooper started to go through the routine with him, but he claimed not to have been in the area before. He let the man go, but Fry stopped when he was a few yards past them.

‘I didn’t like the look of him,’ she said. ‘We ought to check him out properly.’

‘Why? He’s probably just a bird-watcher or something.’