‘Joe,’ I say as calmly as I can. ‘You mustn’t hit Mummy. That really hurt.’

He wriggles out of my arms then turns and runs towards the staircase, the blanket in his arms.

I go after him, but he’s running so fast I can hear his footsteps on the stairs. Then I hear something: a faint humming noise which grows louder as I approach the staircase.

‘Oh what fun tis to ride …’

‘Jingle Bells’. Joe is still singing it.

‘That’s a lovely song,’ I call out to the empty passageway. ‘Now shall we go and light the fire and make some cocoa? Then we can sing some more Christmas songs. What do you say?’

I pause at the foot of the stairs and listen. There’s a clatter of footsteps overhead and then he starts to giggle.

‘Come on, Joe,’ I call up the stairs. ‘It’s too dark to play hide and seek. Now come downstairs and we’ll get a nice hot drink.’

The footsteps intensify, loud and heavy like he’s dancing or jumping up and down.

‘Joe,’ I call, my voice louder and firmer. ‘Please come down. Now.’

The footsteps stop. I wait for him to emerge at the top of the stairs, my heart pulsating in my chest, but there is no sign of him.

‘Joe?’

I realize I will have to go up there and get him. It’s dark and he could fall and injure himself. Gripping the banister with my right hand, I slowly make my way up the stairs, calling to him as I go.

‘Coming ready or not,’ I cry, trying to keep my voice steady as I shine the torch ahead of me. ‘No more hiding, baby.’

The air smells stale and cloying as I go further up the stairs and as I reach the landing a cloud of thick dust hits me and I start to cough. Putting my hand to my mouth, I slowly make my way along the narrow passage.

There’s a half-closed door ahead of me and as I shine the torch at it I see that the walls and floor inside have all been painted white. I blink to adjust my eyes but the glare of white makes me feel dizzy and disorientated.

‘Joe,’ I call as I step towards the door. ‘Joe, where are you?’

I take hold of the door handle, my mouth dry and clammy, and then I hear it again. The song. But something about it sounds wrong. It’s a distorted sound, like an old LP being played on the wrong speed. And then I realize it’s not Joe’s voice I can hear singing, it’s something much more disturbing. The voice behind that door, growing louder and louder as I stand trembling with fear, my hand gripping the handle, is a man’s voice. I need to get Joe out of there. Now.

‘Joe,’ I cry as I push the door open and burst into the room, shining the torch in front of me. ‘Joe –’