Concern pricked at her, questions needling her brain. Would the girls expect her to creep downstairs and open the front door rather than risk making a noise trying to climb through the window? She dare not think how her father would react if he discovered what they’d done.

She checked the clock. 9 p.m. At least an hour until the disco finished. No need to worry yet. Sara thumped Shannon’s pillow and propped it up against the headboard, helped herself to a slice of leftover pizza and began to read again.

She couldn’t be sure when she first realized something was wrong. Ten minutes later, perhaps fifteen. And it was more of a feeling than a knowing. She placed her book down, pages splayed across the duvet, and slipped off Shannon’s bed, fingers trailing greasily across the cotton.

Sara stood in the centre of the bedroom, quiet as a mouse, and listened.

She could hear the drowsy night-time song of roosting birds and the occasional rumble of a car driving through the village, and the distant lowing of cows in the cattle shed down the lane. She could hear the shriek of a mating vixen and the groan of the hot water pipes, and the faintest drift of classical music.

A floorboard on the landing outside Shannon’s bedroom creaked.

All at once, above the sounds of the night, she could hear a ringing in her ears and the push of blood through her veins and the quickening of her breath.

The noises in Sara’s head were as loud as a rushing river and she willed her body to quieten itself. She stood as still as she could manage, straining to listen, trying to dismiss it as a trick of her imagination or the bones of the old house settling to bed.

After a few seconds – although to Sara it felt much longer – she began to relax, to assume that she must have been mistaken. She was fiddling with the make-up brushes on Shannon’s dressing table, dusting blusher across her cheekbones, when something made her spin around, a crushing feeling in her chest.

Because there it was again, the creak of a landing floorboard that confirmed someone was standing outside the door.

Her gaze flitted to Shannon’s bed, realizing too late she had forgotten to put back the pillow that was supposed to pass as her older sister’s sleeping body. Too late to turn the radio on.

Fear tightened its cold fingers around her throat.

She had just enough time to pull shut the door to Shannon’s tiny en suite bathroom before the bedroom door opened and Mrs Carter walked in.

She was carrying a glass of wine in her hand and an expression that Sara knew well.

‘Hi, Pamela,’ she said brightly, an antidote to the gathering clouds of her mother’s anger.

Her mother stared at the pizza box on the bedroom carpet.

‘Put that in the bin.’