A sandstorm batters the Sonora Desert in Mexico. Two vehicles arrive and discharge Mayflower Project operatives including David Laughlin, who explains that he is not a professional interpreter, but a cartographer. However, Laughlin translates for French scientist Claude Lacombe as project members rush to a mysterious circle of vintage WW II airplanes, which were reported missing in 1945. Meanwhile, in Indianapolis, Indiana, air traffic controllers monitor a strange aircraft in the vicinity of two airliners. There is a near miss, but the pilots don’t want to report an Unidentified Flying Object (UFO). Elsewhere, in Muncie, Indiana, a young boy named Barry Guiler is awakened by the wind. As his toys begin to operate independently, Barry goes downstairs, where he is delighted to find the front door is open and the house bathed in bright light. Barry’s mother, Jillian Guiler, awakens to see Barry running into the woods. Nearby, Roy Neary is at home with his wife, Ronnie, and their three children when the phone rings. Ronnie is told that there is a widespread power outage and Roy is to report to work at a substation. As Jillian looks for Barry in the woods, Roy parks on a country road, lost. Lights appear behind Roy’s truck and levitate as mailboxes shake and the truck loses power; gravity is momentarily reversed, then everything goes quiet. Roy sees a spacecraft flying away and drives after it while Barry runs down a road on Crescendo Summit and encounters a family watching the sky. Jillian finds Barry and grabs her son just as Roy’s truck comes around a bend, narrowly missing them. Three low-flying spacecraft fly past, followed by three police cars. The UFOs fly through a toll collection area, cross into Ohio, and disappear into the distance as electric power is restored across the valley. With his face half-sunburned, Roy heads home to collect his family and drives them back to Crescendo Summit, hoping to share another UFO event with them. The next morning, Roy is fascinated by the mountainous shape of his shaving cream and later receives a phone call terminating his employment. Despite Ronnie’s protests, Roy goes back to Crescendo Summit that night and gathers with fellow UFO witnesses, including Jillian and Barry, whom Roy observes making the same mountain shape in the mud that he saw earlier in his shaving cream. Although the crowd is excited by approaching lights, the aircraft turn out to be helicopters. Across the globe in India, Lacombe and his team record thousands of people chanting a series of musical tones. When asked where the sounds came from, the people point to the sky. Back in the U.S., Lacombe shares his breakthrough with an auditorium audience and demonstrates hand signals that correlate to the musical notes. A satellite dish in Barstow, California, beams the tonal sequence into space and a signal of repeating numbers is received in response. Laughlin, the cartographer-turned-translator, notes that the first set of numbers is a longitude and the team determines that the location is in Wyoming. Meanwhile, in Muncie, Barry plays the same notes on a xylophone while Jillian sketches the mysterious mountain. Taking out the trash, Jillian sees rolling clouds and the bright lights of an approaching spacecraft, then runs inside and barricades the house as it rattles. Despite Jillian’s efforts to grab hold of her son, Barry crawls away through the dog door and disappears. Sometime later at a U.S. Air Force briefing, Major Benchley and the Mayflower Support Leader debunk the sightings; however, a team of people in red jumpsuits and sunglasses are loaded on a bus in an unidentified military warehouse. Reviewing a map of a Wyoming mountain called Devil’s Tower, military personnel, including Major “Wild Bill” Walsh, debate possible cover stories to evacuate the area without prompting suspicion. Back at the Neary home, Roy continues to be haunted by the mountain shape; he sculpts it with mashed potatoes at dinner and later builds a clay model, but remains bewildered. In the morning, Roy knocks the peak off of his clay mountain in defeat and the flat plateau triggers recognition. After uprooting plants and collecting debris from neighbors’ yards, Roy’s obsession frightens Ronnie and she gathers the children to leave for her sister’s home. Constructing a mountain from mud, Roy watches television and notices a breaking news report about a train derailment in Wyoming that supposedly unleashed nerve gas. When the footage depicts a mass evacuation near Devil’s Tower, Roy is elated to recognize the flat-topped mountain of his imagination. Meanwhile, Jillian sees the same report and connects the Devil’s Tower to her own obsessive drawings. Sometime later, Roy drives a rented station wagon to Wyoming, where he rescues Jillian from being evacuated on a train. As Roy speeds away from the military checkpoint, Jillian updates him on the search for Barry. Arriving at a barbwire barricade, Roy and Jillian see Devil’s Tower in the distance and marvel at the mountain that had previously only existed in their minds. Continuing on the road, they observe what appear to be dead livestock; although Roy believes the evacuation is a government hoax, they don gas masks to be safe. Soon, the car is stopped by military vehicles. Roy and Jillian are separated and detained by soldiers dressed in hazardous material suits. Lacombe and Laughlin interrogate Roy, asking if he has had a “close encounter” and showing him photographs of eleven people, including Jillian. At a base camp below Devil’s Tower, Roy and Jillian are reunited on a helicopter with the ten other people who sought out the mountain, but Roy is convinced that the air is not contaminated with nerve gas and takes off his mask to prove that the story is a hoax. Meanwhile, Wild Bill Walsh berates Lacombe for allowing civilians into the restricted area; however, Lacombe defends the UFO witnesses and suggests that there may be thousands more. Back at the helicopter pad, Roy, Jillian, and a comrade named Larry Butler escape and soldiers give chase. Maj. Walsh orders helicopters to spray the sleep aerosol previously used on the area’s livestock to make the animals appear dead. Although the sleeping gas fells Larry, Roy and Jillian get away and discover a well-lit arena with a landing strip on the backside of Devil’s Tower. As scientists make preparations, lights appear in the distance and move toward Roy and Jillian. When four spacecraft fly over the arena, project members play the tones that Lacombe discovered in India and Jillian recognizes the tune from Barry’s xylophone. After repeating the musical sequence in response, the spacecrafts fly away and the scientists break into applause. As more spacecraft swarm overhead, Roy wants to get closer, but Jillian is afraid to continue. After kissing his companion farewell, Roy climbs toward the landing strip. In a moment of silence, an enormous mother ship arrives, casting a dark shadow. While the notes are reciprocated between the scientists and the spaceship, Jillian follows Roy into the arena. As the craft lowers its ramp, radiating a warm glow, figures materialize in the light, including the WW II pilots who went missing in 1945 and Barry, who runs to Jillian. Lacombe and the officials discuss Roy as a potential human representative for the spaceship’s next voyage and Lacombe admits envy. The spaceship’s ramp opens again, revealing a spider-like creature and other humanoid aliens, and an official asks Roy for his full cooperation. Following a church service, the team of astronauts in red jumpsuits walks toward the mother ship with Roy in tow, but two aliens pull Roy out of the line and lead him aboard the craft. When an alien exchanges hand signals with Lacombe, a calm falls over the observers. The mother ship ascends into the sky, with Roy aboard, and disappears into the darkness.