On a visit to London, eighteen-year-old American Melinda Greyton (played by seventeen-year-old Brit Dame Elizabeth Taylor) goes to her first party, a Regimental ball. There she meets and falls madly in love with Major Michael Curragh (Robert Taylor), a handsome bachelor who returns her affections. After a relatively short period of time, they marry and all is bliss. Michael has some peculiar habits such as when he gets upset when Melinda sends an old overcoat out for cleaning, or when she takes a few one pound notes from his wallet. In fact, Michael is a Communist spy and has been a member of the Party since he was in school. When Melinda finally realizes just what and who he is, she tells him to choose between her or his beliefs. He tells her he'll leave the Party, but it's all a ruse. He does love his wife, however, and when his spy masters tell him Melinda must be done away with, he faces the ultimate choice.