Drums in the Deep South (1951)

Before plantation wife Kathy Summers (Barbara Payton) can run off with her lover, Clay Clayburn (James Craig), civil war breaks out and he must report to the Confederate Army. However, within a few years he returns to Georgia, and Kathy is still in her old home -- which the Union Army, led by Clay's best friend, Maj. Will Denning (Guy Madison), is using for a base. Kathy begins spying for Clay, but she struggles with the idea that one of these two friends may kill the other in battle.