In 1839, visitors from miles around come to Kentucky to tour Mammoth Cave. But sixteen-year-old Charlotte, the maid at Mammoth Cave Hotel, doesn't understand its appeal. As a slave, she is already trapped, and she doesn't see the point in risking being trapped underground as well. Still, she's curious when Stephen Bishop, another slave who is the cave's expert guide and chief explorer, makes some big discoveries underground, and she's interested in...