The sound came again, cutting through the night: a sharp metallic tap that carried even to the first floor of the house where Sam lay sleeping. Ella stood over him and listened for it again but all she heard was rain spattering against the window. There was a storm coming – a fine start to the summer holidays – but that wasn’t the problem.

The problem was being alone in the house at ten o’clock at night looking after Sam. She wished now that Fin hadn’t slipped out to see Billy but it was her own fault: she’d insisted he go, telling him Mum and Dad would never know as long as he was back before they returned from the pub.

But that could be ages. Billy’s parents had gone with them, which meant Mum and Mrs Meade would be yakking non-stop and Mr Meade would be trying to talk Dad into buying a new car from his showroom or joining the Save-the-Lighthouse project. They wouldn’t leave the pub before eleven and Fin would take his time, especially as she’d promised him she was all right.

But she wasn’t all right. She was terrified.

The sound came again, downstairs. She crept to the door. At least she hadn’t undressed for bed. She’d been thinking of it but she was still in the jeans, T-shirt and trainers she’d slopped around in all day, and now she was glad of it. It made her feel less vulnerable – though only a little.

She glanced at Sam. He looked so peaceful as he slept. She didn’t remember sleeping like that when she was three and now, at thirteen, she hardly slept at all. She was scared of the dark, scared of the noises she heard in this ancient house, and now, after Mr Fenner’s lecture in assembly about the need to be vigilant with strangers, she was even scared someone was stalking her round the village, though she knew that must be ridiculous.

Tap! The sound came again. She knew she ought to go down and investigate. Fin would. He might be small for fifteen but he’d go straight down and look the thing in the face. She made herself walk to the head of the stairs. Below her, the hall stretched away in eerie stillness. The lights were on but the house felt oppressive.

There’s nothing wrong, she told herself, and started to walk down the stairs. It’s just a storm coming. But it was no use. Polvellan was a house that had always frightened her even though she’d lived here all her life. It wasn’t just that it was such an old building. There was something else, something she didn’t understand; she felt uneasy here even when the others were around.

Tap! The sound snapped in the night again. She opened her mouth to call out and ask if anyone were there, then closed it again. If somebody were in the house, the last thing she should do was give herself away. She thought of Sam and wondered whether to go back and guard him.

No, check the downstairs rooms first. Make yourself do it. Then go back to Sam.

She tiptoed to the foot of the stairs and looked about her. On the wall nearby was the photograph of Dad at the opening of his Newquay superstore. Next to it were the sketches he had made of the Pengrig lighthouse ten years ago before the cliff-falls made it an endangered building. She ran her eye nervously over them, then scanned the hall as far as the front door.

Tap! She gave a start and looked to the left. The noise had come from the sitting room. There was no doubt about it. She stared at the door; it was ajar and the lights inside the room were switched off. She reached for the telephone. Ring Billy. Get him to send Fin home.

But she drew her hand back. She had to master this. She had to check the noise out for herself. It was bound to be something simple. She walked to the sitting room door and gave it a push. It brushed over the carpet a few inches and stopped. She stared through the gap, then took a deep breath, pushed the door a little further, and craned her head round.

The old room looked dusky but reassuringly familiar. Behind the drawn curtains she could hear the rain lashing against the window; but at least there was no one here. She pushed the door fully open and switched on the light. The features of the room sprang into focus: the piano, the fireplace, the armchairs, the sofa, the music stand with her flute beside it. She walked into the room.

Tap! She jumped. It was the window. Someone must be out there, hidden by the curtains. She hurried to the phone, picked it up and started to dial nine-nine-nine; then put it down. This was stupid. The tap wasn’t regular. It might not be a person at all; it might be something trivial. What would Dad say if she called the police out for nothing? She strode to the window, pulled back the curtain, and burst out laughing.

It was nothing after all. A chain from one of the hanging baskets had broken loose and gusts were throwing it up at the window so that every so often the metal ring at the end struck the glass. Tap! There it was again. She chuckled and reached out to close the curtain; then froze in horror.

Reflected in the glass was a figure standing behind her in the doorway.

She whirled round. It was a man, a huge man built like a bear. He wore a black oilskin top and black waterproof trousers, all gleaming wet, and blue sailing shoes. The hood was up and fastened tight round the face, which was half-obscured by a scarf over the mouth and nose. She took a step back.

‘Don’t hurt me. Please don’t hurt me.’

The eyes stared darkly at her.

‘What do you want?’ she said.

‘You,’ came the answer.