My heart throws itself against the walls of my chest. Adrenalin sings in my blood. Driven not by bravery but by instinct, I run back up the stairs, along the narrow landing and into her bedroom. The curtains are open and the moon is watching with her dispassionate eye.

The present throws me back to the past. I’ve been here before. The slippery smell of blood. A rawness in the air. Butchered meat and old keys. Except this time it’s not a twelve-year-old girl in daisy-print pyjamas, but a woman with grey streaks in her hair and eyes the colour of dust.

The steel blades of the scissors in her hand are dulled by a slick of blood.

Shannon Carter smiles at me, and mumbles something about a hero.

Sara is lying on the bed. Blood soaks the sheet. Her face is pale, her eyes lock mine.

As I stand there, hesitating, Shannon lifts the scissors, high above her head, and Sara screams again, a long, high note striated with fear. The memory of her mother’s screams echo down the years until all I can hear is the song of their suffering, and I want to run from the Carter sisters, who bring death with them.

But Sara is bleeding, and if I run, she will die, so I grab Shannon’s hair and pull sharply.

Her head jerks backwards but she does not let go of the scissors, and instead turns and slashes at me, half blinded by night.

But the pale blur of my skin gives me away and the point of the blade catches my arm, and there’s a fire, white-hot, above the inside of my wrist, and a wetness that stipples the carpet with dozens of dark spots.

I stare, disbelieving, at the mess of my arm and she stabs me in the shoulder.

‘Stop it, Shannon,’ I say, in painful understatement. But she shakes her head and laughs.

When I look down, the loops of the scissor handles are sticking out of my body. The burn of pain is deadened by adrenalin and a surge of fury that this woman – this stranger who once meant everything to me – has killed someone I love and lived the life that should have been Sara’s.

And then I realize she’s gifted me a weapon.

The scissors are slippery between my fingers, warm with blood. Pulling them out has opened up the wound. Shannon is watching me and watching Sara, her eyes flicking between us both. She doesn’t speak, but carries an aura of righteousness, a belief that she is following the path of her destiny.

‘Please,’ I say. ‘Let us go.’

‘No,’ she says. Cocks her head in consideration. ‘If I did that, what would happen to me?’