Near the top of the track he noticed a crumpled Coke can, dropped by some careless visitor. Muttering angrily, he picked it up and slipped it under the flap of his rucksack, where it joined a small pile of chocolate bar wrappers, aluminium ring-pulls and an empty Marlboro packet and some cigarette ends he had found near the Hammond Tower, to be disposed of later. Mark couldn’t tolerate the attitude that made people think it was OK to scatter the environment with litter. They thought their own convenience was more important.

If he had his way, Mark would ban these people completely from the national park. He would put tollgates on all the entrance roads and issue passes for admission. It might come to it one day, too. The park couldn’t cope with the constantly rising numbers.

There were tyre tracks in the sandy soil here. That meant there had been a mountain biker this way recently. Mark knew his by-laws; he had read the regulations carefully, and he knew what was allowed and what wasn’t. The Peak District National Park Authority had prosecuted mountain bikers before.

He smiled in satisfaction, then immediately felt guilty. Owen said the main skills you needed as a Ranger were tact and diplomacy. Why get into an argument when you could achieve more with a friendly word of advice? Mark knew he had a lot to learn. Sometimes he couldn’t find the right things to say to people who appalled him with their stupidity and their disregard for their own safety, the property of others – and, above all, for the environment and its wildlife. That was their greatest crime, these people who desecrated the moors. The last thing they deserved was diplomacy.

Though it was only two o’clock, it would be starting to go dark in a couple of hours’ time. For a few days now, Mark had noticed that peculiar half-light, like full moonlight, that came at five o’clock in the afternoon, when all the colours seemed to change and glow for a few minutes before fading into the darkness. The turning back of the clocks at the end of British Summer Time always worried the Peak Park Rangers. Walkers were liable to miscalculate and still be on the hills when it went dark.

The afternoon was turning cold, but Mark didn’t feel the chill. The red fleece jacket he wore proudly, with its silver Peak Park insignia, kept him warm. It was also a reassuring sight for the visitors a Ranger came across – those who were lost and bewildered, exhausted or injured, or simply inadequately dressed and too poorly equipped for walking the moors. The sight of the red jacket was like a friendly beacon. It meant a Ranger approaching.

Jenny Weston had been in the act of smiling when she died. Her smile had stiffened and shattered, twisting into a grin of fear as the knife slipped under her ribs.