“Way up at the top of the cavern,” Jet said, “there’s a skylight—an opening in the ceiling. For a short time each day, when the sun is high, light streams in. It hits the crystals, which makes them glow in the dark for hours afterward.” Jet came in for a landing next to Sophie. “My grandpa says it’s called photoluminescence.”

“Your grandpa?” Owen said. “Does he live here too?”

Jet nodded. “My whole family lives here,” he said. “See!”

He pointed to an area high up on the cavern wall. Dozens and dozens of bats hung upside down from crystal ledges.

“Wow!” said Hattie. “You have a big family!”

“Yep,” the bat replied. “Brothers, sisters, my mom and dad, aunts, uncles, cousins, and grandparents. They’re all here!”

A couple of the bats waved hello. But most hung there motionless. Their wings were wrapped tightly around their bodies as if they were in sleeping bags. They peeked out at the visitors with curiosity.

“They’re not used to company either,” Jet explained. “It’s kind of why we live in here. It’s peaceful. And quiet.” Then he laughed. “Well, usually it is,” he added.

Sophie nodded. Then it hit her. The bat family would probably prefer to be left alone.

“Well, we should get going,” said Sophie. “We all have homework to do, anyway.”

Owen was staring dreamily into a crystal. “We do?” he said.

But Hattie understood. “Yep, we do,” she said, nudging Owen toward the exit. “Jet, could you help us find the way out?”