Doc explains that, after an accident in his bathroom in 1955 where he hit his head, he had a vision of the flux capacitor. Though it took 30 years of research and most of his family's fortune to develop it, the project is a success and Doc plans to travel through time. As he talks to Marty, Doc absently sets the vehicle's destination time to that date. When Marty asks what the DeLorean runs on instead of gasoline, Doc tells him it needs plutonium, explaining that a nuclear reaction is necessary to generate 1.21 gigawatts to power the flux capacitor.
Marty is alarmed, asking where the Doc could possibly have gotten such a substance and Doc tells him that he hired a couple of Libyan terrorists to steal it for him with the promise of building them a bomb. Doc, however, cheated them, delivering a fake bomb. Doc and Marty, clad in yellow radiation suits, load another pellet of plutonium into the DeLorean and Doc begins his farewell address to Marty and the camera. Just then, a Volkswagen van races into the parking lot.
A man pops out of the roof with an AK-47 and begins shooting. Doc yells for Marty to run; in the van are the Libyans that Doc cheated. Doc tries to hide as well but that is when the Libyans' van comes to a stop in front of him. Doc throws away his revolver, showing that he intends to surrender, only for the Libyan to shoot him full of holes. Marty tries to hide but is found as well; when the Libyan tries to shoot him, his rifle jams.
Marty jumps into the DeLorean and races off, the van close behind. As Marty swings back into the parking lot, he decides to see if the van can do 90 mph. As he races towards a photo kiosk, Marty fails to see the speedometer creeping toward 88 mph or the fact that the time clock is set to November 5, 1955. Suddenly, there is a flash of light and the kiosk and parking lot are replaced with an empty grassy field, and the car plows right into a scarecrow. Marty is startled, loses control of the DeLorean, and crashes into a barn full of cows.
The noise wakes up Otis Peabody and his family, who live in the farmhouse next door, and they come outside to investigate the noise. When they open the barn doors, they are shocked at what they find: an airplane without wings has crashed on their property. Peabody's son Sherman decides that the DeLorean is actually an alien spaceship, showing a comic book. Just then, the driver's door lifts up and Marty climbs out, still clad in his radiation suit. Peabody and his family scream in terror, thinking Marty is an alien, and flee towards the house.
Marty attempts to apologize for the damage, when suddenly Peabody returns with a shotgun and begins shooting at him. Marty jumps back in the DeLorean and speeds out of the barn, Peabody continuing to shoot at him. As Marty flees down the dirt path leading to the road, he inadvertently plows through one of two small pine trees lying next to the path and protected by a picket fence. Peabody shoots at the car, in the process destroying his own mailbox, shouting, "You space bastard! You killed our pine!"
Marty reaches the two lane road and speeds off, muttering that the experience must be a nightmare, heading for home. When he gets to Lyon Estates, he finds the stone gates marking the entrance to the neighborhood, but to his surprise, instead of a street lined with houses, there is just an empty grassy field with several construction vehicles sitting idle.
A large billboard advertises the future housing development that is breaking ground next winter. Marty, still clad in his radiation suit, sees a car coming along the road and attempts to hitchhike, but the occupants are scared by Marty's suit and continue driving. Discovering that the DeLorean is out of gas, Marty removes his radiation suit and pushes the DeLorean back behind the billboard to hide it from passing motorists, then notices a sign reading "Hill Valley: 2 Miles."
Marty is next seen walking into the courthouse square of downtown Hill Valley. Hill Valley of 1955 is a lot different to Marty. The courthouse square is an actual garden instead of a parking lot. The Essex movie theater is showing Cattle Queen of Montana instead of a porno film. The Texaco station is a full service station where attendants not just fill up the tank but also wash the windows and check the customer's engine and tires.
A mayoral campaign car drives around the square, blaring "Reelect Mayor Red Thomas!" Most importantly, the clock tower is still functioning, as indicated when Marty is surprised to hear its half hour chime. Marty still believes that he is in a dream, but realizes this is reality when he picks up a newspaper tossed into a trash can and sees the date "November 5, 1955" on the top of the paper.
Marty steps into Lou's Diner (which is the outlet for an aerobic class in 1985), at this point only inhabited by Lou Caruthers, the owner, and another customer eating breakfast at the counter. Marty goes to the phone booth and looks up Doc's address in the phonebook, tearing the page out so he can look it up later. As Marty tries to ask for directions, Lou demands that Marty either order something or leave. Marty gets himself some decaf coffee after misunderstandings about Pepsi Free and Tab. After Lou sets a coffee cup down in front of Marty, we now notice that the customer Marty is sitting next to is his future father.