The film starts in February of 1979, at a steel plant in Lillian, Ohio. Elizabeth Lamb (Caitriona Balfe) has been killed in an accident.
Though their family and friends are sad for her husband, Deputy Jackson Lamb (Kyle Chandler), their main concern is Joe Lamb (Joel Courtney), Elizabeth and Jackson's son. Joe was more attached to his Mom than his Dad, who has never really been there for his son.
Later at the Lamb's house, Louis Dainard (Ron Eldard) pays a visit. Jackson blames Louis for his wife's death, and forces him out of the house and puts him in his squad car. As Joe watches his father take Louis away, his gaze shifts to a silver locket in his hand.
Four months later, the local Middle School lets out for the summer. Joe's friend Charles (Riley Griffiths) has been shooting a Super 8 film for a film festival in Cleveland. Charles has rewritten the story so that the detective now has a wife.
Joe is unsure about this last-minute rewrite, but when Charles tells him that he has gotten Alice Dainard for the part (Elle Fanning), he becomes less-concerned. The two then promise to rendezvous later that night to film their scene, with plans for Alice to drive them.
Arriving home, Joe meets up with his Dad who takes him out for dinner. Jackson Lamb wants his son to attend a baseball camp for the summer, but Joe explains that he wants to help Charles finish his film. Both reach a impasse, having little more to say on the matter.
Later that evening, Joe goes to meet Charles and the rest of their crew: Cary (Ryan Lee), Preston (Zach Mills), and Martin (Gabriel Basso). When Alice shows up in her Dad's Buick Skylark, she's concerned that 'the Deputy's Son' knows she's driving without a license. Joe promises not to tell, and Alice reluctantly allows him along for the ride.
The group arrives at the Lillian Train Station, where Charles intends to shoot a scene with Martin as the detective of his story, trying to get his wife (aka Alice) to leave because of a zombie infection.
Joe is smitten with Alice, who shocks the guys when during the rehearsal, she delivers a performance that brings her to tears. The boys are snapped out of their shock by the sound of an approaching train. Charles demands they start filming again ASAP so they can put the train into their film and increase the 'production value.'
As they film the scene of the train thundering past the station, Joe catches sight of a white truck turning onto the tracks. The truck hits the train, causing a massive (and explosive) derailment. The gang runs for cover, and luckily survive the ordeal. Joe hears something pounding loudly on one of the derailed train cars right before the door flies off.
Surveying the wreckage, they come across some strange white cubes (Joe takes one), and find the wreckage of the truck. Inside, they find the body of one of their local science teacher, Dr Woodward (Glynn Turman).
Joe removes a map from the doctor's hand. Everyone is shocked when he starts talking to them. Pulling a gun, he threatens them and tells them that they are not to tell anyone what they saw.
Suddenly, the sound of men approaching the wreck catches their attention. Fearful of being caught, they recover Charles' Super 8 camera, and quickly drive off. In the car, everyone is panicked about what just happened, and Alice says her coming was a mistake.
Analysis of the camera the next day reveals that it the lens is broken; however, Charles and Joe drop off the film for development. Joe insists he will help Charles finish the film, offering his Dad's video camera. However, Charles believes that Alice will most likely not want to help them after the night before.
Joe goes over to Alice's house to convince her to help them finish the film. Their conversation is interrupted by the arrival of Alice's father. He demands that Joe stay away from the family's home and Alice. Seeing that her father is somewhat drunk, she agrees to help Joe and his friends.