What is the plot of The Day the Earth Stood Still?

Directed by Robert Wise, the 1951 science-fiction classic The Day the Earth Stood Still follows an alien visitor named Klaatu who lands his flying saucer in Washington, D.C., accompanied by his robot servant, Gort.1

After being shot and hospitalized, Klaatu escapes and befriends a widow named Helen Benson and her son. He reveals to a scientist, Professor Barnhardt, that he represents a federation of planets and has come to warn humanity that its development of atomic weapons threatens the safety of other civilizations.1

To demonstrate his power, Klaatu causes a global power outage. Ultimately, he warns Earth’s leaders that they must abandon violence or face destruction by other planets in self-defense. The film is noted for its reflection of Cold War anxieties and its innovative score by Bernard Herrmann.1