During the American Civil War, five northern prisoners of war decide to escape, during the siege of Richmond, Virginia, by hijacking a balloon. There is no safety visible beneath them, as the gas falls and the balloon loses altitude. The windswept, watery expanse presents not a single speck of solid surface upon which their anchor might hold. That they are riding in this gondola beneath the balloon is already an act of desperation — for they are prisoners of war, who hit upon this mad scheme for aerial escape: the theft of the balloon moored and awaiting abatement of the storm, to ride with it directly up into those turbulent clouds! Through rare luck and ingenuity, the escapees manage to keep the balloon above the waves until a speck of land comes into sight, and within reach . a piece of uncharted and unknown land that promises safety and survival — but which presents life-threatening challenges and holds at its heart a supreme mystery.