In November 1955, moments after witnessing
Emmett "Doc" Brown disappear in his
DeLorean,
Marty McFly learns that Doc was sent 70 years in the past to 1885. Using information from Doc's 1885 letter, Marty and the 1955 Doc find and repair the DeLorean, hidden away by Doc in 1885, so that Marty can return to 1985. After finding it, Marty comes across a tombstone inscribed with Doc's name, stating that Doc was shot by
Biff Tannen's great-grandfather, Buford "Mad Dog" Tannen, six days after writing the letter. Despite the letter's warning, Marty travels to September 2, 1885, to save Doc, arriving in the middle of a
cavalry pursuit of
Native Americans, but the car's fuel line is damaged. Chased by a
bear, he is knocked unconscious and found by his
Irish-born great-great-grandparents
Seamus and Maggie McFly, who allow him to stay the night. The next morning, under the alias
Clint Eastwood, Marty arrives in a newly founded
Hill Valley but runs afoul of Buford and his gang. Doc rescues Marty from Buford's attempted
lynching. Doc agrees to leave 1885 after learning his fate, but without gasoline, the DeLorean cannot reach its required . He proposes using a
steam locomotive to push the DeLorean to that speed. While inspecting a
rail spur, Doc saves the town's new schoolteacher
Clara Clayton from falling into the ravine, averting her death from the original timeline. They fall in love. At a town festival Buford tries shooting Doc, but after Marty intervenes, Buford challenges him to a showdown in two days by calling him "
yellow". Doc urges Marty not to react to provocation, letting slip that Marty has a life changing accident in the future. Although reluctant to return to 1985, Doc visits Clara to end their relationship and bid her goodbye. She dismisses his story about being from the future. Doc goes on a
drinking binge. Buford arrives for Marty, who sees his alias appear in the tombstone photograph and refuses to duel. Doc passes out and is captured by Buford's gang, forcing Marty to duel. Marty feigns death and knocks Buford into a wagon of
manure. Buford and his gang are arrested for an earlier robbery. On the train to
San Francisco, Clara learns how heartbroken Doc is and runs back to town. She finds the model time machine at his shop and realizes Doc was telling the truth. Doc and Marty use the locomotive to push the DeLorean along the spur line. Clara boards the locomotive and loses her footing. Marty, in the DeLorean, passes his
hoverboard to Doc, who uses it to save Clara. The DeLorean hits 88 mph and vanishes as the locomotive plunges from the unfinished bridge. Arriving back in 1985 on October 27, Marty escapes the disabled DeLorean as a freight train destroys it. Reuniting with his girlfriend
Jennifer Parker, Marty declines a street race with
Douglas J. Needles, thus avoiding the future accident Doc warned him about. Jennifer opens the fax message she kept from 2015 and watches the text regarding Marty's firing disappear. As Marty and Jennifer examine the DeLorean wreckage, a steam locomotive time machine appears, operated by Doc, Clara, and
their children. Doc gives Marty a photo of them standing next to the town clock in 1885. When Jennifer asks Doc about the blank fax, he says it means their future has not yet been written and encourages them to make it a good one. Doc and his family bid farewell and fly off in the locomotive. ==Cast==