From the other side of the flimsy door his loud, blurry voice demanded, ‘Who’s this?’

‘Colin, it’s Sadie. From the bookbinders.’

There was a silence. Another voice, a woman’s, called something I couldn’t catch from further inside the flat and Colin answered, ‘It’s all right, Mum. I’m getting it.’

There was another silence. I put my thumb to the bell and leaned on it.

‘All right. All right, hold your horses,’ Colin muttered. There was the sound of bolts being slid back, then the door opened on a chain. His spectacles and thick nose appeared in the gap.

‘It’s me, Colin. Let me in.’

‘I can see it’s you. You can’t be too careful, you know.’

He took the chain off and unlocked the grille. I edged into the tiny hallway, with Paul right behind me. It was very hot in there and thick with Colin’s body odour. There was a framed picture of the young Queen, in tiara and garter sash, on the wall.

‘Who are you?’ Colin demanded.

‘My name’s Paul. I’m Sadie’s friend.’

I sidestepped very slowly and carefully towards an open inner doorway. I could hear the plink-plink of a child’s musical box. The sweat on my back had turned icy.

The cramped room was almost entirely filled with a sofa and a huge television.

On the sofa Cassie was sitting, wide-eyed, gripping the musical box. Beside her was a little old woman, her teeth bared in a smile that was almost a grimace. Her gums were bright pink and shiny, revealing them to be old-fashioned dentures.

‘Sadie-lady,’ Cassie said. She let the musical box drop and slid off the sofa. Her plump legs made a squeak against the sofa’s plastic covering. The old woman caught the discarded toy and set it carefully on the sofa arm. I saw that there were framed photographs on the walls, the windowsill and on top of the television, all of them of a little girl.

I held out my hand to Cassie, smiling at her as calmly as I could. With the other hand I extracted my mobile phone from my pocket and gave it to Paul. He stepped smoothly back into the hallway. I held Cassie’s warm, sticky hand in mine for a second, then I stooped down to her level. ‘Hello,’ I whispered. I couldn’t see any fear or pain reflected in her wide brown eyes. She looked surprised and mildly curious.

There was no sign of the red swimsuit. She was dressed up like a living doll in a lemon-yellow smocked-front dress with a matching hand-knit cardigan, tiny white ankle socks and white leather bar shoes. Her hair had been combed flat and centre-parted, and fixed with hairgrips and bows of lemon-yellow ribbon.