American films, like America itself, have long been fascinated by the threat of outsiders posing as citizens to destroy the American way of life. This book tracks real-world fears appearing in the movies--Nazi agents, Japanese-American spies, Communist Party subversives, Islamic sleeper cells--as well as the science-fiction threats that play to the same fears, such as alien body-snatchers and android doppelgangers. The work also examines fears inspired by World War I German spies, the Japanese-American internment and the McCarthyite witch-hunts and shows how these issues, and others, played out on screen.