In 1928, on an expedition in the snowy mountains of India, a mountaineer encounters a glowing sphere. He touches it and then finds himself awakening after a sudden loss of consciousness, with the sphere now gone and a scar on his hand.
In the present day, the United States government hastily assembles a group of scientists, including Princeton professor Dr. Helen Benson, to formulate a survival plan when it is feared that a large unknown object with a speed of approximately one-tenth the speed of light, is due to impact Manhattan in approximately 78 minutes.
The object slows down just before impact and is revealed to be a large spherical spaceship, which lands gently in Central Park. A being named Klaatu emerges from the sphere, around which the military has established a perimeter. Amidst the confusion, Klaatu is shot. A gigantic robot emerges, emitting a sound that temporarily paralyzes humans and disrupts all electrical systems in New York City. Before the robot can take the being back, Klaatu orders it to shut down.
While recovering from his injuries, Klaatu takes on the appearance of the man from the opening scene of the film. He informs Regina Jackson, the United States Secretary of Defense, that he is a representative of a group of alien races sent to talk to the United Nations. Jackson instead orders that Klaatu be sent to a secure location. Klaatu manages to escape with the help of Helen, and is pursued by the authorities throughout Newark, New Jersey, and the forested Highlands, with Helen and her stepson Jacob.