The story unfolds in February 1979 at a steel plant in Lillian, Ohio, where a tragic accident claims the life of Elizabeth Lamb (Caitriona Balfe). Her husband, Deputy Jackson Lamb (Kyle Chandler), grapples with profound grief, yet the community's focus shifts primarily to their son, Joe Lamb (Joel Courtney). Harboring resentment, Jackson blames Louis Dainard for Elizabeth’s untimely death, forcibly ejecting him from their home and into his squad car. As Joe witnesses this, his attention is drawn to a silver locket clutched in his hand.
Fast forward to summer, where Joe's friend Charles (Riley Griffiths) is filming a Super 8 movie for a festival, casting Alice Dainard (Elle Fanning) as the detective's wife. On the day of the shoot, they arrive at the Lillian Train Station, with Charles eager to incorporate an oncoming train into their scene, aiming to elevate the film's quality. While filming, a terrifying event occurs: Joe spots a truck veering onto the tracks, culminating in a catastrophic train derailment. The group narrowly escapes the explosion, but not without hearing something ominous pounding against one of the wrecked train cars.
Venturing through the wreckage, they discover unsettling white cubes and the remains of a local science teacher, Dr. Woodward (Glynn Turman). In a panic, Joe grabs a map from the deceased's hand, while the atmosphere thickens with fear when a gun is drawn, compelling them to remain silent about the grisly event. On edge, they recover Charles' Super 8 camera, racing off before anyone can discover the truth.
The following day, Charles and Joe develop their film, with Joe promising to assist using his father's video camera. However, Charles doubts Alice’s willingness to join after the previous night’s chaos. When Joe visits Alice's home to persuade her to help, tensions rise as her father, Louis, prohibits him from entering. Nevertheless, sensing his father’s inebriated state, Alice agrees to aid Joe and his friends in completing the film.
Their adventure leads them back to the site of the train crash, where Joe notices the train showcasing Air Force insignia. Later, while examining the map from Dr. Woodward, he recognizes a peculiar red line running across the country. As panic engulfs Lillian with news of missing people and bizarre occurrences, Sheriff Pruitt (Brett Rice) vanishes, and Jackson Lamb becomes increasingly suspicious of the military as they start to appear, performing a mysterious cleanup operation.
Jackson confronts General Nelec (Noah Emmerich) over the government’s secrecy regarding "Operation: Walking Distance." When the military’s presence intensifies, townsfolk report missing household items, deepening the mystery surrounding these bizarre events. His investigation leads to an unexpected arrest at the airfield, thwarting his quest for answers.
Meanwhile, Joe and Alice's bond deepens. After she witnesses her father's aggressive antics and narrowly escapes abduction, Joe and his friends realize the danger encroaching on their town. They discover film evidence revealing the creature’s existence—a being from another world, more intelligent than initially assumed, striving to return home. These revelations fortify their resolve.
As the military mobilizes, chaos descends upon Lillian. Tanks rumble through the streets while the boys discover the creature's lair beneath the town’s water tower, finding missing townsfolk—including Alice! Utilizing fireworks as a distraction, Joe and his friends mount a daring rescue, culminating in a tense confrontation with the creature.
As tensions rise and hope dwindles, Joe bravely confronts the creature, choosing empathy over hostility, marking a turning point in their relationship. With the families reunited, a poignant climax unfolds as something extraordinary transpires at the water tower—the locket Joe held is central to a larger narrative of loss and acceptance, ultimately allowing the creature to return to the skies.
In a captivating post-credits scene, we see Charles’ completed film, titled The Case, work as a particularly emotional capstone to their journey, intricately weaving the supernatural elements with the trials of youth and friendship, drawing viewers back to the thrill of childhood creativity amid chaos.
