In 1915 Vienna, the Great War has caused many casualties. Elsa decides to answer the patriotic appeals and help by working in the hospital, but her reputation causes her to be rejected. Because of her past, military intelligence wants her to find out whether an army major is spying for the allies. She meets the major at a dinner and they agree to meet later, but before she can keep the date, she is courted by a young naval officer named Karl. Falling in love, she ignores her spying assignment, but knows that she can never tell her new love about her life. When Karl has a chance to go on a heroic mission, Elsa sends him away with a "Dear Karl" letter. However, the paths of these three people cross again and she decides what she must do.