‘Yes, and a keen walker. Fit for his age, too. But he was walking on his own, and he seems to have stumbled into the rake in the fog.’

‘There’s a fence, though.’

‘He climbed over it – you can see his boot prints are right there. He must not have realized what was on the other side, poor sod.’

Cooper looked down at a damp blue object lying on the ground at the officer’s feet.

‘Is that his rucksack?’

‘Yes. He wasn’t heading far, but he came well equipped.’

‘Where was he staying?’

‘Middleton Dale. He told the owner of the B&B that he was going to walk up to Wardlow and back.’ The officer shook his head. ‘I know it was really foggy. But all he had to do was keep going in a straight line, and he would have reached the road, no problem.’

‘In fog, the loss of visual clues destroys your sense of direction,’ said Cooper. ‘In open ground like this, the tendency is to go round and round in circles. I reckon that’s what he must have done.’

‘At least the weather has kept most of the public away. No casual passers-by to disturb the scene. All you need with an incident like this is fifty members of the Healthy Life Rambling Club trampling through the scene with their fell boots and hiking sticks.’

‘But he was found by walkers?’

‘Three nosy retired bobbies.’

Cooper drew a damp wad of paper out of the pocket of the rucksack and carefully unfolded it on the ground.

‘What’s that?’ asked Irvine.

‘An Ordnance Survey map, Luke. Outdoor Leisure series, White Peak area.’

‘He should have been able to find his way with that, shouldn’t he? They’re incredibly detailed. Every slope and contour line is on them. Every field boundary.’

‘Yes, two and a half inches to the mile. You’d think it would have helped him, even in dense fog.’

When Cooper unfolded the wet mass, he discovered a cover picture of Dove Dale, one of the Peak District’s most popular limestone valleys, photographed in the summer, of course, with a few strollers by the riverside. And the cover of the map bore a price: £2.95.

‘This is an old edition of the OS map,’ he said. ‘Yes, look – last revised in 1979. It’s thirty years out of date.’

‘Does that make a difference?’

‘Well, compare it to mine.’ Cooper drew his own map from a pocket of his coat. ‘I’ve got the most recent edition, reprinted in 2006. There’s Middleton Dale, just the same. And Black Harry Lane going up across the moor to Black Harry Gate. But then, see – in this big hollow –’

‘Blimey,’ said Irvine. ‘There’s a lake.’

‘A flash. Flooded quarry workings. On the old map it shows “Brandy Bottle Mine (Disused)”. But the mine has gone from the new map. The workings filled up with water, and the OS took it into account when they did their revisions.’