He could hear rain falling in the black canal, spitting and hissing as it hit the water’s surface, but he stayed strangely dry. The path was empty, except for a pile of rubbish. Whatever had happened here was over. It wasn’t what he was looking for. Callum ran on past the shapeless tangle of shopping trolleys and mattresses.

Suddenly he was running through utter blackness, as though he’d entered a tunnel. It was like running with his eyes shut, but he didn’t hit anything. Once he glanced up, and there were stars overhead, then he was plunged back into the darkness. Callum rubbed his eyes until red spots flashed against his eyelids.

A shriek of pure terror split the night. The noise drove into Callum’s head like an iron spike. Although his heart pounded with fear, his feet and legs reacted automatically, turning towards the sound. That was the way he had to go.

But now he was in a different city. Somehow he had travelled hundreds of miles, running in the starlit dark, but there was no time to stop and wonder how. Cars lined the streets. Terraced houses flashed past on either side, charmless but ordinary.

Then the voice cried out again:

‘Help me!’

‘Where are you?’ Callum yelled. ‘I’m coming!’

When the next scream came, it was one of mindless agony.

Abruptly, Callum turned a corner into a narrow alley. The high brick walls of urban back gardens rose steeply on either side of him, still echoing with the terrible scream. All the gates were shut and locked. The windows of the houses beyond were dark. The pavement was lined with cracks. Grey, patchy grass straggled through the gaps.

This was the place. Callum knew it the moment his bare feet touched the cool, tacky concrete. But now everything was still and quiet; not even the echo remaining.