Doc has written Marty a letter saying that he must leave him in 1885 and instead just go back to 1985. Doc in 1955 is supposed to help him get there.
Marty and Doc find the DeLorean, in an abandoned mine. As they are leaving with the car, Capurnicus (Doc's dog in 1955) barks at a grave and won't leave it alone. Marty goes over and discovers that it's Docs grave! He gets gunned down by Bufford 'Mad Dog' Tannen, exactly one week after he wrote the letter! He was shot over a dispute for $80.
Marty goes to 1885 to save him. When he arrives he meets his Great Great Grandparents. The first McFly's in America. Marty goes into town and see's 'Mad Dog' in the local saloon. Marty calls him Mad Dog and Bufford tries to kill him. Marty gets chased to the clocktower (Which is still getting built). He is about to be hanged when Doc saves him. Marty and Doc decide to leave straight away, but there is no petrol. They have to figure out a way to get home before Doc is killed!
They try pulling it to 88mph with horses but don't get close. So they decide to push it to 88mph with a train. At this time Doc falls in love with Clara Clayton. They are going to the Town Festival. Bufford is there and he tries to kill Doc. Marty saves him. Bufford challenges Marty to a shoot out. It is going to be on at the same time as they leave to go back to the future!
Doc tells Clara that he's from the future! She of course doesn't believe him. Doc goes to the saloon and stays there all night talking about the future. The next morning Marty finds him there. Just when they are about to go Doc drinks his first drink for all night and passes out.
Bufford arrives ready for the shoot out. Doc wakes up and they try to sneak out the back. Doc is captured and Marty has to come out or Doc will be killed.
Marty comes out drops his gun and says "I thought that they could settle this like men." Bufford says "You thought wrong dude." And shoot him. Marty falls over dead. Bufford comes over laughing. Marty stands up! Bufford punches his stomach and nearly breaks his hand! Marty has had a door of a stove under his poncho to be his bullet-proof vest! He takes it off and belt Bufford around the head! Bufford falls into a manure cart!
Doc and Marty leave for the train. They get on and stop it. Clara finds the model of the time machine and chases after the train too. As Doc is getting into the car Clara blows the whistle of the train. Doc goes back for her on the hoverboard. Marty goes to the future without Doc!
When he gets to 1985, a train runs over the DeLorean and destroy's it. Marty shows Jennifer. Then Doc arrives in a train! He shows Marty and Jennifer his kids and tells them that there future is whatever they want it to be. It isn't already written for them! Doc flys of into another time, in the train.
The End.
