I loved this book so much right up until almost the very end. There will be some serious spoilers later, but for now, I’ll merely give an overview. A group of men crash their balloon near a deserted island in the South Pacific during the Civil War. They manage to make their way through the rough surf to a small islet off the coast of a larger island that has been formed by a volcano. At low tide, they cross the strip of sea between the two and begin to explore the larger island. They eventually find their engineer, who was lost in the ocean during their crash. It would seem that he’s been saved by some mysterious benefactor who put him in a cave to recover.