Based on the 1948 novel Conspirator by Humphrey Slater, the film is about a beautiful 18-year-old American woman who meets and falls in love with one of a British Guards, an officer who turns out to be a spy for the Soviet Union.

While visiting England, 18 year old Melinda Greyton attends a Regimental Ball where she meets handsome Major Michael Curragh.

After much discussion Michael decides to pretend to give up that life, but soon discovers the party orders him to kill his wife.

The producers were careful to cut mentions in the film of the British traitors during the Second World War, such as John Amery and Norman Baillie-Stewart, out of fear of litigation by their families.

[citation needed] When "Melinda" is asked her age by "Aunt Jessica", Elizabeth Taylor's voice says "18", but her lips say "16".