Somewhere deeper down, a bare electric bulb came on.

I went carefully down a short flight of steps, smelling damp and dust, and then I was under the house itself, the ceiling so low that I had to stoop.

Mallory’s voice was right behind me: ‘Anything?’

The basement was more than half full with scrap, smashed chunks of concrete and broken bricks, a ragged pile of rubble that almost reached to the ceiling.

‘What is all this stuff?’ I said.

‘Looks like someone dreamed of converting this place into flats,’ Mallory said. ‘They have to fill the basement. Fire regulations. Then the property bubble burst and the dream got cancelled.’ He peered into the darkness. ‘Excuse me,’ he said, easing past. ‘There’s something right at the back.’

‘Clear,’ I heard someone call at the top of the house. Then a brief gale of laughter, like a collective sigh of relief. They seemed very far away.

Mallory moved towards the back wall of the basement. There was a scuttle of something small but living across the rubble and I felt my heart lurch. The tail of a fat rat slithered over the rusted frame of a child’s bicycle.

‘There’s a door,’ Mallory said, and he suddenly had his torch in his hand, a sharp white beam in the dull yellow darkness.

PC Greene was now halfway down the steps, staring at Mallory’s back. We both followed him.

Mallory was trying the door.

Locked.

Then the lights went out. All of them. The mains. A switch had been thrown. I could hear voices protesting far above us.

Mallory had some sort of blade in his hand and was running it inside the doorjamb. I took his torch and held it on the door as he moved the blade left and right, left and right, lifting the lock tongue from the doorframe socket until he had it.

The door opened with a crack of wood. Beyond it was a metal grille. And from somewhere beyond that came the screams of a woman.

Help me help me help me help me help me.

The rattle of a metal grille in the blackness.

‘You hear that?’ Mallory said.

‘Yes.’

We were talking in whispers now. Mallory was reaching through the grille. It was locked from the inside. But a set of keys jangled on a nail; and then he had them and the grille suddenly slid open.

‘You smell it?’ Mallory said.

‘Yes, sir, I can smell it.’

The stink of shit and petrol.

‘Careful in here,’ he said, stepping inside.

I followed him and I felt the ground beneath my feet, rough and uneven, and the screaming was louder now and it was recognisably Scarlet Bush, and we moved more quickly because the space suddenly opened up and I was between Mallory and Greene when Mallory seemed to lurch forward and I grabbed a fistful of his jacket and stopped him falling.