As the Freeman family leaves a park after watching the South Florida Frisbee Dog Championship, twelve-year-old David Freeman announces that someday his dog, Bruiser, will win the Frisbee competition. However, his younger brother, Jeff, thinks their dog is feeble and winning would be a long shot. Soon, Jeff is dropped at a friend’s house, and the Freeman family arrives home. After dark, Helen Freeman asks David to escort Jeff on his walk home through the woods. The brothers meet but when Bruiser runs off, David searches for his dog, slips, and falls unconscious into a ravine. He awakens and returns to the house without Bruiser. He finds the front door locked and pounds on the door. A strange woman appears and asks who he is. He runs past her looking for his parents. The house has been redecorated and his bedroom is now a study. The homeowners call police to reunite David with his parents. At the police station, Detective Banks and a colleague pull a missing persons report on David dated 1978. As the officers drive David to his parents’ new address, David believes the year is 1978 and Jimmy Carter is the president of the United States. His answers are met with silence. They stop at an unfamiliar house. When Bill and Helen Freeman greet the detective at the door, David rushes to meet them. As his parents embrace him in joy and disbelief, David loses consciousness. Elsewhere, Dr. Louis Faraday of The National Aeronautics Space Administration (NASA) has been called to examine an alien spaceship tangled in an electrical tower. As Faraday ponders how to move the spaceship to a new location, David is scared as he is wheeled through a hospital hallway. His mother promises that no harm will come to him, and a doctor calls his parents away. David thinks he was only gone for a few hours, but sees his brother, Jeff, now a teenager, standing by the door. Jeff describes how David went missing eight years ago, and every weekend, their parents insisted Jeff post missing person flyers with David’s photograph. As he hands David a flier, he says it is 1986. His parents return, and say the doctor wants to run some tests. David tells his mother that if he has truly been away eight years, it seems like a bad dream. Later, Dr. Faraday and his team transport the alien spaceship in a flatbed truck to an empty airplane hangar. At the hospital, David wakes and tells Jeff that he hears a voice over and over but does not understand the words. Reassured by Jeff that he is not going crazy, David falls back to sleep. At NASA, Dr. Faraday and his team are unable to penetrate the spaceship. Later, the doctor attaches electrodes to David’s head, and another doctor interviews him about his adventure in the woods. As he speaks, his brain waves create linear drawings of a spaceship on a computer screen. His doctor forwards the drawings to Dr. Faraday at NASA. Soon, Dr. Faraday visits the Freemans and asks that David be put under his care. David refuses until the doctor suggests he can explain the mystery behind David’s disappearance. He asks David to spend two days at NASA so the staff can determine the truth, and he agrees. As David rides with Dr. Faraday, he hears alien voices the doctor cannot detect. David is sequestered in a bedroom with toys, and a state-of-the-art television set. Soon, intern Carolyn McAdams delivers dinner in an automated food cart, and discovers David has missed out on recent popular culture. Later, more electrodes are attached to David’s head and he is interviewed. As David responds, scientists notice alternate answers appear in English on their computer screens, but soon, the answers switch to an alien language, and Dr. Faraday addresses the screen directly. It responds that the trip from the planet Phalon took 2.2 solar hours. Then, the screen scans though several uncharted solar systems until it locates Phalon. The computer activity upsets David, who pulls off the electrodes and runs away. Back in his room, Carolyn McAdams reveals to David that his stay has been extended. He persuades her to contact his parents to rescue him. At night, David hears alien voices asking for his help. He hides in Carolyn’s automated food cart and escapes undetected by guards. The food cart transports him to the hangar where the alien spaceship is stocked. As he circles the mollusk-shaped craft, liquid metal pours from a hatch and forms a floating staircase. Slowly, he climbs the stairs and enters the vessel. There, Max, a robot pilot, admits to summoning David, and ushers him into a chair that rises from the floor. David possesses information Max needs to complete his mission. Max calls him “the navigator,” and explains that he must access navigational charts that have been stored in David’s memory. His own data was wiped out when he plowed into an electrical tower. When instruments reveal security has been breached, NASA staff descends on the hangar. Dr. Faraday commands David to leave the ship. Instead, NASA scientists watch helplessly as the spaceship breaks free from its mooring with David inside. When David orders the pilot to travel twenty miles away, Max directs the ship twenty miles above Earth. Exasperated, David gives an order to return to his planet. They land in a field surrounded by cows. There, David learns that Max’s mission is to study species from other planets. After he studied David it was too dangerous to send him back in time so he returned him to the place where David was found. David will let Max have the charts he needs, if Max returns him to his family. However, helicopters carrying NASA scientists appear, and David orders Max to escape somewhere they cannot be found. Max submerges the spacecraft underwater and David is introduced to other specimens Max collected. The animals are hungry, and one grabs David’s NASA cap and devours it. Once Max scans David’s memory, he absorbs much American culture and sounds increasingly human. David makes the mistake of calling Max a geek, and the robot shuts down the engines. As the craft plunges to Earth, David discovers how to fly the spaceship. Meanwhile, Dr. Faraday wants to talk to Carolyn McAdams because she was the last person to see David, and finds her at the Freeman house explaining to David’s family what has happened. Soon, David and Max are lost. They travel from Japan to San Francisco, and scare some travellers on the road when they stop to ask for directions. David teaches Max a Beach Boys song as they head toward Florida. From the air, the spaceship reaches Al’s Gator City, and David deduces they must be in Florida. After landing, David borrows change from Al to use the payphone. He talks to his brother Jeff and asks him to devise a signal that can be seen from the air so he can navigate his way home. David flies the ship, following Turnpike signs to Fort Lauderdale. Meanwhile, Jeff climbs to the roof of the house with a box of fireworks. The first few rockets he ignites malfunction, but then a few launch and colors burst in the night sky. Bill and Helen stand on their front lawn watching for the spaceship. As David sees the fireworks and lands, NASA scientists and police surround the house. David steps out of the craft and says he no longer belongs with his family and apologizes to his parents. He ducks inside the spaceship and leaves. He tells Max he knows he should be with his family but he belongs back in 1978. Max tells him that a return to the past might bring about his death, but David has to try. The ship goes back in time, and David wakes up in the ravine. When he reaches his front door, his parents call to him from their boat dock. As he steps onto their boat, David tells his mother he loves her, hugs Bruiser, and tells Jeff he loves him too. Jeff notices a tiny alien creature sticking out of David’s backpack. David pushes the creature back and silently motions Jeff not to say anything. In space, Max says to David, “See you later, alligator!” David gazes up at the sky and smiles.