In 1865, during the American Civil War, a massive storm sweeps through a Confederate States of America prison camp. Union (American Civil War) soldiers Cyrus Smith (Michael Craig (actor)), Herbert Brown (Michael Callan) and Neb (Dan Jackson) are planning an escape via a gas balloon tethered next to the compound. When a new prisoner, Union war correspondent Gideon Spillet (Gary Merrill), is brought into their cell, they knock out the guards and escape from the prison house. Once they arrive at the balloon, they drag one of the Confederate guards named Pencroft (Percy Herbert (actor)) aboard. After he explains that he knows how to pilot the balloon, they let him join the group.