|In 1955, Marty McFly and Doc Brown use the information in Doc's 1885 letter to retrieve and repair the damaged DeLorean (which has been waiting for him in a mineshaft for 70 years). As they retrieve the car, Marty spies a tombstone with Doc's name, dated six days after the letter. Learning Doc was killed by Biff Tannen's ancestor, Buford "Mad Dog" Tannen, Marty decides to go back to 1885 to save Doc and bring him back to the future.
|Marty arrives on September 2, 1885, in the middle of a United States Cavalry pursuit of Indians. Unfortunately, an arrow has ripped a hole in the fuel line, emptying the gas tank and rendering the DeLorean engine useless. Furthermore, Doc falls in love with the local schoolteacher, Clara Clayton, and considers staying in 1885. Marty must convince Doc to come back with him and find a way to get back to his time before it's too late.
|Buford tries killing Doc at a town festival but Marty intervenes; Buford then goads Marty into a showdown in two days' time. Doc reluctantly decides to return to the present with Marty. With the fuel tank in the DeLorean empty and gasoline unavailable, he devises a scheme to use a locomotive to push the DeLorean up to speed.
|The night before their departure, Doc, despondent about his lost love, returns to the town saloon to get drunk. Marty rides to the saloon and convinces Doc to leave with him, when Buford arrives and demands the duel to take place immediately. Marty realizes his reputation is unimportant and refuses to fight. But Buford's gang captures Doc. Marty uses a steel door to a furnace as a bullet-proof shield, and knocks Buford out. With Buford no longer a threat, Marty and Doc steal the locomotive.
|Meanwhile, Clara discovers Doc's model of the time travel experiment and rides after him. She boards the speeding locomotive and climb out to Doc while he is climbing towards the DeLorean. Unfortunately she falls off the side, hanging by her dress. Doc uses Marty's hoverboard to save Clara. They coast away from the train safely as the DeLorean disappears through time with Marty.
|Marty arrives safely on October 27, 1985, but the powerless DeLorean is destroyed when a freight train strikes it head-on. Marty returns to his home, discovering that everything has returned to the improved timeline. Marty finds Jennifer sleeping on her front porch. Later, Marty uses the lessons he learned in 1885 to avoid being goaded into a street race, avoiding the potential automobile accident which would cause more downward turns for the McFly family in the future.
|Marty takes Jennifer to the time machine wreckage. They worries that Doc has been lost in the past forever, when suddenly Doc Brown appears in a new time machine modeled after a locomotive with Clara (to whom he is now married) and their two sons. Doc tells Marty and Jennifer that the future has not been written yet, and that it is "whatever you make it, so make it a good one." After the Browns bid farewell to their friends, Doc's train converts into a hovertrain and roars off into an unknown time.
（China.org.cn Rebecca 译）