She had been sitting for some time on the landing window seat, a slim volume in her lap, watching the rain assault the leaded panes. When Miss Ireland, the headmistress, asked her to find Camilla, the youngest girl in the school, Louisa was glad of something to do.

In a dusty lobby at the back of the building, where the games equipment was kept, Louisa turned, with difficulty, the corroded iron handle of a large studded and blackened door and stepped cautiously through the opening. It was surprisingly warm as she descended the stairs beyond. The walls she passed were of rich golden rock, not the cold grey stone one might expect in a cellar. At the foot of the stairs a tunnel curved away from Louisa, sloping downwards, its floor uneven and treacherously slippery in places. Windows had been carved through the sandstone rock to the outside of the cliff on which the school stood, but the curtain of rain allowed through little light to illuminate the underground room. At the lowest part of the tunnel Louisa stopped and, instead of continuing up the few steps to the door which led to the outdoor games pitches, she turned to the back wall. Here was an elevated gallery with pillars carved out of the rock, close together. In a ballroom they would have been magnificent. Here in the dark cave, they loomed oppressively. Swallowing the feeling of dread they always gave her, Louisa pulled herself up to the ledge and slipped between two of the pillars. Beyond, huddled in an archway hollowed from the rock, was the miserable figure of a young girl.

"I thought I might find you here," Louisa said.

The girl looked up, displaying a tear-stained face. "Louisa? Is it you? I'm not going back!"

"Do you dislike us so much, Camilla?" Louisa asked gently.

"Not you," said the girl, with a sob. "You're nice. You're the only nice thing in this whole horrible place. Horrible Nottingham, horrible Miss Ireland, horrible Howard House School! And it's rained every day since I came! Even down here, all you can hear is the rain!"

It was true. The rain drummed all around them, a gentle thunder in the rock. As they listened, it became louder. Camilla clutched at her friend as the clamour mounted. "I'm frightened!"

Louisa peered between the columns as the noise became more deafening. There was an ominous sweet odour in the cave. With an explosive crack the door to the pleasure-grounds burst open as a torrent of floodwater gushed through.

"Camilla," she yelled. "We have to get out of here!"

She grabbed the child's arm and hauled her to her feet. Beyond the pillars, however, the floor of the cave room was in turmoil as water poured in, pounding the rock walls, sending waves against the columns and dashing sprays of icy water against the two girls' bodies.

As the torrent slackened, Louisa began to lower herself into the water, hoping to wade towards the stairs leading up to the school. The water was already too deep. She could see the pale square that was the nearest window, water lapping its ledge. Even if they could get to it, it was thickly glazed and did not open.

Camilla helped her struggle back behind the pillars.

"Follow me," the girl said. "I know where we'll be safe!"

Camilla had disappeared in the darkness at the back of the cave before Louisa had wrung enough water out of her skirts to be able to follow her. As her eyes adjusted to the darkness, she was just able to see her friend. Staggering on, she fell, and found herself face to face with a fearsome creature, rearing in the darkness. Louisa screamed, then realised that it was a carved lion, with disordered mane and bared teeth. Behind it was another, and another, and she could just make out a gigantic figure, with raised arms, further back.

Camilla, astride a lion's head, begged her friend to sit down, and Louisa was only too glad to comply. "They'll come and look for us soon," she said, wearily. "Or else the water will go down. There must be several ways it can run out of the cave."

"I think we're sitting on a sculpture of some kind," the younger girl said. Now, she seemed almost to be enjoying herself. "I don't know if anyone else knows it's here. I found it all by myself."

Wet, entirely chilled and gagging on the putrid dank smell the water had brought, Louisa was unexpectedly cheered by Camilla's irrelevant conversation. "A man and some lions," she said thoughtfully. "They must have been carved long ago, before Howard House became a school."

Talking comforted them, as the noise of the water gradually subsided and an uneasy silence fell. Strangely, there was more light in their corner, reflected off the now still surface of the water in the tunnel. Then, blessedly, they heard splashes, and a voice, calling their names. Louisa picked up her wet skirts and went to peer through the pillars again. She could distinguish the struggling forms of two men, up to their waists in water and connected by ropes. A black shape on the school stairs, above the water level, seemed to be Miss Ireland, calling them.

Louisa shouted and waved and, as the nearest man waded in her direction, saw an unfamiliar light cross the surface of the water.

"You won't believe this," she called to her friend, "I can see sunshine. The rain has stopped at last!"