At first it was the darkness that made Jemima wish she hadn’t come. Percy, leading Clement and her, had the only torch and when they’d crept a little way into the cave, she could see nothing but the halo of light encircling his head. Elsewhere was a blackness so impenetrable that she could screw her eyes closed and open them again and not notice any change.

The darkness began to press in on her. It felt like she was shuffling through a narrow tunnel, causing her to hunch her head into her shoulders. She knew this was silly. When Percy directed his torch upwards or from side to side, she was able to see the cave’s roof and walls were as high and wide as the inside of a barn. But the darkness made her uneasy. And when she was nervous she felt a strong need to talk. She resisted the urge, however. She didn’t want Percy and Clement regretting that they'd allowed her to tag along.

Next it was the cold. Outside the summer sun was shining and like the boys she’d dressed for the weather – in a thin cotton shirt and shorts. She hadn’t expected the cave to be so deep or the air in it so chilly. They’d only been walking for five minutes and already she was shivering.

Finally, there were the bats. Percy was leading them across a sandy section of the cave’s floor when his probing torch happened on them – hundreds of them, hanging from the roof like a crop of blackened fruit.

“Look!” he’d exclaimed.

Disturbed by his shout, the bats took to the air in a swirling confusion of fluttering wings and rat-like bodies. Jemima screamed and crouched down as they swarmed overhead. When the whirring of their wings died away she raised her head and was dazzled by Percy’s light. He shifted the beam onto Clement, who was squatting alongside her with his hands clasped over his head.

“What are you two doing?” he asked.

“What’s it look like?” said Clement. “We’re making sure those dive-bombing whatsits don’t fly into us.”

They heard Percy chuckle.

“Those were bats,” he said. “And they won’t fly into you. They’ve a built-in radar that tells them exactly where you are.”

“Well, they’re one up on me,” said Clement. “I haven’t a clue where I am.”

“Don’t worry, we aren’t lost,” Percy reassured him. “The way out is that way,” he said, shining the torch behind them.

“Haven’t we gone far enough?” asked Jemima through chattering teeth.

“It is a much deeper cave than I imagined,” Percy conceded. “But the end can’t be too far off. You don’t want to stop now, do you?”

“I am a bit c-cold.”

“Me too,” said Clement.

“Oh!” Percy sounded disappointed. “Let’s just see what’s over that rise,” he suggested, directing the torch’s beam up the gradient ahead of them. “Then we’ll go back and prepare for a proper exploration, with lamps and warm clothes and everything. Agreed?”

Jemima and Clement looked enquiringly at each other before shrugging resignedly and falling in behind him once more as he began picking his way up the rock-strewn incline.

He was nearing the top of this slope when a whir of wings jerked his attention and the torch beam towards the ceiling once more. Afterwards, when she reviewed the ensuing sequence of events, Jemima couldn’t help thinking that anybody else would have halted to take in the cloud of bats swirling above his head. But this was Percy – geeky, gawky, head-in-the-clouds Percy. With his head tilted back, he’d stumbled blindly onwards. For a few steps his upper body was silhouetted against the light; then with a cry and a clatter of stones the cave was plunged into darkness. Percy was gone.