But in this case, what he hadn’t noticed was that he and Matt, gazing solemnly out of the screen, were standing right in front of the giant policeman in the main building of the arboretum. The bobby loomed over them, vast and ominous, blocking out the light from the windows like a monstrous ghost.

He’d also been much too tall for the lens of Claire’s digital camera. The head and helmet of the giant policeman were neatly sliced off.

PHILIP WORSLEY HAD finally admitted to himself that he was lost. The fog had come down so quickly on Longstone Moor that it had confused him totally.

When he’d set off to walk from Stoney Middleton, the weather had been clear, and he’d taken advantage of a spell without rain for his late afternoon walk. He couldn’t believe that it was so different up here – so different that he could barely see his hand in front of his face. This didn’t happen back home in Essex.

At one point, Philip thought he’d reached the path that led downwards to the crossroads. There was supposed to be a farmhouse not far from the junction, though he couldn’t tell which direction it lay in. He’d been here before, years ago, and it was a pity that his memory wasn’t clearer. He’d have to hope for a distant light visible when he got nearer.

He had a map in his rucksack, of course, but none of the landmarks seemed to fit. Nothing was where it was supposed to be. A slope where it should be flat, water where there should be land. It was as if he’d stepped out of the real world into some parallel universe.

He shivered in the damp fog. And for the first time, Philip started to feel concerned. Apart from his map, he had a waterproof, a bottle of water, a spare pair of socks in case he got his feet wet. But nothing to eat, except a roll of his favourite sweets, the perfumed Parma Violets that he’d remembered from his school days. There might be some sugar in them, but they wouldn’t provide him with extra energy for long.

Philip kept walking, but without recognizing any signs or gateways. Twenty minutes later, when his foot slipped into a hole and his ankle doubled up underneath him, he knew he wasn’t on the path at all. For the last few hundred yards, the slope of the land had been tending upwards, not down. The ache in his calf muscles was enough to tell him that fact, but he’d been trying not to notice it.

As he nursed his painful ankle and wiped a bloodied scratch on his hand, he knew that he was now in difficulties. He had no idea what direction he’d been walking in, or whether he’d even set off from the place he thought he had twenty minutes ago. His ankle wasn’t actually sprained, and he could still walk on it, if he was careful. But the fog was as thick as ever, and there were no lights visible, no sound of traffic from any direction. His senses detected nothing around him except muffled rustlings and coughs in the heather, sounds that he took for the presence of sheep.