The two teen runaways, Seth and Sara, are actually extraterrestrial beings who have landed on Earth and are trying to find their way back home to their planet. They possess powers such as telekinesis, telepathy, and the ability to phase through objects.
The people who are after them are government agents and scientists who want to capture and study them. The duo manages to sneak aboard a spacecraft hidden in a secret government facility, and the taxi driver, Jack Bruno, is coerced into helping them get to Witch Mountain, where their spacecraft is located.
As they race to Witch Mountain, they encounter various obstacles and dangerous situations, including a dangerous alien assassin sent to kill them. Along the way, they also uncover a conspiracy involving the government agents and a powerful corporation that wants to exploit the extraterrestrial technology for their own gain.
Eventually, Seth and Sara make it to Witch Mountain and are able to repair their spacecraft with the help of Jack. They bid farewell to Jack and take off into space, leaving behind a grateful and awe-struck taxi driver.