The film begins with Dr. Helen Benson being summoned to a military facility with several other scientists when an alien spacecraft of sorts arrives in New York City. On board is a race of aliens and a giant robot of enormous size and formidable fighting abilities. The aliens call themselves Klaatu and say he has come to save the Earth.  However, subsequent interrogation methods lead Klaatu and those behind him to decide that humanity must be wiped out in order for the Earth to survive.