Ambitious television reporter Tim O’Hara (Jeff Daniels) stumbles upon a real-life Martian (Christopher Lloyd) whose space ship has crash-landed on Earth. Believing this is the story of the millennium and his chance for a Pulitzer Prize, Tim makes plans to expose the Martian who, posing as Tim’s Uncle Martin, takes human form with plans of his own.

Obviously, Uncle Martin doesn’t want to be identified. In fact, all of Tim’s efforts to divulge the truth are systematically thwarted by the resourceful alien who ultimately recruits Tim to help him repair his ship for a return to Mars. They eventually become pals and join together to overcome the many hilarious obstacles that confront them along the way.