He slipped through the door on to a wooden walkway over the water channel. This area was open to the air, filled with the noise of the river and the sensation of empty space all around and above him in the darkness. The water that had once driven the mill’s waterwheels still ran the turbines, and it flowed fast under the walkway here. He could hear its rush and feel the vibrations of the current.

But beyond the end rail was a stagnant basin. His torch picked out iron chains hanging from ancient pulleys, coated with dust and cobwebs. The chains disappeared into the murk, reaching down towards mysterious shapes that he barely glimpsed in the depths, metal structures with a forgotten purpose. Cooper shivered as he saw bits of dead vegetation floating on the surface. Even an adult might have difficulty in that water. Imagine getting tangled in the chains and dragged to the bottom.

His torchlight illuminated a warning sign. But was it the fast-flowing goyt it was warning of? Or the still, dark basin with its shadows below the surface?

Cooper turned sharply to the left, not sure what he was reacting to. His senses were confused by the adjustment from the silent interior of the mill to the noise outside. A series of explosions reminded him that the fireworks display was still going on over the village. The cascade of coloured light helped him to orientate himself. Beyond the goyt he could make out the bank of the river, and directly in front of him was an area of slippery concrete channels and sudden drops into black, lethal water.

It didn’t feel any safer out here than it had inside. Of course, he ought to let Fry know where he was. So Cooper tried his phone again. But he was down by the river now, with the vast bulk of the mill behind him and the limestone crags towering on both sides. He raised his phone to head height and moved it in a different direction. No signal.

The roar of the weir sounded much louder at night. Now that he was close to it, it almost drowned the crack and scream of the fireworks launching from High Tor. Cooper strained to listen for sounds of movement above the rush of water from the weir and the hum of the turbines in the mill. The only other noise he could hear was a tap-tap-tap against the side of the channel as a polystyrene cup bobbed on the surface of the water. Tap-tap-tap on the concrete walls.

He thought he heard a shout somewhere, a woman’s voice. But the words were incomprehensible. He was almost sure he saw a shadow flickering, and caught the rustle of a long skirt on concrete.