Andie might have guessed. As punishment for going to the Stones concert, she wasn’t to be allowed out with Kris for the next few days. “And then,” Mum stipulated, after tea, “only if you tell us where you’re going, and come back at the time we agree and not a moment later.”

“So it’s all right for Prune,” Andie grumbled, “but I do exactly the same thing and get clobbered for it?”

“Andie, Prue’s sixteen,” said Mum. “So’s Sushila. I can’t say I’m delighted about them going, either – but there’s a big difference between twelve and sixteen.”

“But you’re being so unreasonable!” Andie clattered the cat dishes into the washing-up bowl. “What’s the point of being in London if I’m not allowed to go anywhere? I might as well go back home and stay with Nan, if I’m going to be kept prisoner here.”

“Now you’re being unreasonable,” Mum told her. “Exaggerating ridiculously. No one’s locking you in prison. If the agency doesn’t come up with work for me tomorrow, I’ll take you to Selfridge’s. You need new shoes for school.”

“Don’t want to go to Selfridge’s,” Andie grumped. “’Specially not to buy stuff for school! Not before the summer holidays have even started properly!”

“I know they haven’t. And we’re going to enjoy being here,” Mum said firmly.

“Enjoy! When I’m not allowed out? I bet Marilyn and Patrick aren’t making all this fuss, just for Kris wandering over to Hyde Park!”

“No, I don’t suppose they are. But they’re – well, much more free and easy than we’re used to.” Mum made a tight, prim face. “I don’t think they’re even married. He’s Patrick Sharp, but her name’s Foley, I think she said. All this permissive carry-on we keep hearing about! They’re living together.” She made it sound like a criminal offence. “Not the sort of people we usually mix with.”

“You can say that again. They’re about five hundred times more interesting.”

Mum stood squarely, hands on hips. “Now you’re being rude, on top of everything else. I think it’s high time you were in bed, young lady. And try to get out on the right side, in the morning.”

Andie must have slept for a while – Prune had come in and got ready for bed without disturbing her – but she’d been fully awake for at least half an hour, her mind full of the day’s sights and sounds, excitements and arguments.

And now her eyes were wide open, and her ears straining for a sound from the stairs.

She was sure she’d heard something, a creak, like someone trying not to be heard. Yes – there it was, creeping on up, towards the attic.

A tremor ran down Andie’s spine – excitement, as much as fear. It could be Patrick, going up to fetch something from one of his boxes, or to put something up there. But why would he do that so late at night, when the whole house was asleep? Only if he had something to hide. What if he was an art thief? Andie’s thoughts raced. She imagined Patrick sneaking paintings – small ones, miniatures would be easiest – out of the National Gallery, tucking them inside the front of his jacket. Then he’d store them in the attic until the next dark night, when his accomplice would bring a riverboat to the nearby pier on the Thames, and smuggle them out to sea, to Holland or France…

Or what if it wasn’t Patrick at all, but a madwoman who lived in the attic? Patrick’s real wife, perhaps – the reason he wasn’t married to Marilyn! Andie’s class had read Jane Eyre this term, and her favourite bits had been about Mr. Rochester’s mad wife who roamed the corridors at night and clawed at people with her nails and set fire to bed curtains with the candles she carried. That would be even more exciting than stolen paintings. But if this was the Madwoman of Chelsea, she must be going back to the attic, not leaving it…

There was only one way to find out. Before Andie knew she’d decided what to do, her feet swung out of bed onto the rug and nudged themselves into her sandals. A dim light from the street lamp, filtering through curtains, was enough to show her the bedroom door, and out to the hallway. The door to Mum and Dad’s bedroom stood open; she heard Dad’s snuffles as he turned over.

She mustn’t lock herself out! Looking round for something to hold the door ajar, she found a sort of wooden rack with umbrellas in it. She managed to lift it into place without making a loud thunk, and slipped past it to the tiny, windowless landing outside.

Compared to the grand staircase that swept up from the ground floor to Kris’s halfway place, these stairs were plain and narrow, with a handrail fixed to the wall. After the top-floor landing, where she stood, another flight led to the attic rooms. Looking up, Andie felt the down-draught of dry, dusty air, and shivered. No light was showing. Who – or what – could be creaking round the attic in darkness? And why?

For a second she considered going back in, getting back into bed and forgetting she’d heard anything. Perhaps she hadn’t. Maybe the sounds were only those of an old house settling into itself, creaking under its own weight, settling for sleep. But then she heard, unmistakably, the sound of footsteps above her head.

Slowly, gripping the handrail, she mounted the stairs. On each one she paused, fumbling for the next with a raised foot. Her eyes and ears were boring into the dark, her heart thumping so strongly that she felt it would throw her off balance. At the turn of the stair she stopped and glanced back at the wedged-open door. If a spectral figure appeared ahead, or if someone flew out at her – a madwoman with nails like daggers – she could scuttle back down and in, and lock the door behind her.

Creak – creak. She couldn’t stop the pressure of her feet from making a faint sound, seeming to echo in her ears and up into the roof space.

But what if it were faster than her – the thing up there? It might rush down the stairs and into the flat ahead of her…shut her out…

Now the creaks were answered by the quick light steps of someone above. Someone moving towards her. She froze, unable after all to run back; fear clamped her feet to the stair, her hand to the rail.

A dark figure appeared in the attic doorway, and stopped there.

“Who’s that?” it said, in a quite ordinary voice: certainly not the way she’d expect a madwoman or a vengeful ghost to sound.

“It’s me,” Andie told it. “Andie.”

The figure seemed to nod. “Shh!” it went, and beckoned her to come on up.

More curious than frightened, Andie followed. A torch flicked on, and the dark space sprang into brightness. She was standing, with this other person, on a narrow landing, up in the very top of the house, beneath the slope of the roof. The torch beam turned to her face, harsh and dazzling.

“You gave me a fright,” said the voice.