Susan Murphy (Reese Witherspoon Reese Witherspoon), a beautiful girl who lives in a small town in California, is about to marry his beloved boyfriend Derek Dieter (Paul Luther Paul Rudd). But at this critical moment, she was first hit on the head by a meteorite, and then glowed into a tall, white-haired giant. Her changes scared away her friends and relatives, and then a group of mysterious people armed with weapons captured her and imprisoned her. Susan was taken by the military to a secret base in District 52, where she and monsters from all corners of the earth were called the object of study by scientists. At the same time, a UFO with evil power is approaching the earth at extremely high speed, and the alien Galexha (voiced by Ryan Wilson Rainn Wilson) is threatening to destroy the earth and destroy mankind. The humans rebelled, but their weapons were all defeated in front of Garexaha. The earth is in danger, and people pin their fate on Susan and her monster friends.