On the surface, Marty's mission is to prevent Brown from being killed by the villain who –for our greatest delight- is Biff's ancestor, Buford "Mad Dog" Tannen, but while Marty and Doc try to find a solution to push the DeLorean to 88 mph, destiny puts them in Clara's path.
Consequently, while the central character of the first film was George McFly and the second part focused on the McFly Family, Gale and Zemeckis took the last film as a great opportunity to enrich the character of Doc Brown and close his story's arc through a love story in order to replace the "mad scientist" label by a necessary element of three-dimensionality. The Far West setting perfectly fitted the tormenting desire of Doc Emmett Brown for retirement and a tacit existential quest for love. The Far West is less a setting or an era, than a state of mind, embodying the roots of the American spirit in its purest form, before greed and profit perverted its meaning. But since people were facing less materialistic issues than during the 80's, I guess there was a need to take some distance from these so-called philosophies of successes and a huge step back one century earlier when the 80's followed the Secession War and preceded the Industrial Revolution that would lead to demise of the frontier spirit. This has always been Marty's preoccupation and the thrust of the trilogy but the travels also had the merit to solve some familial issues and help a beloved character to improve something in his life, if anything, the trilogy defines the notion of 'coming-of-age' as the inspirational aspect of the film, its encouragement for success through self-improvement. This continuity helps to appreciate the second part that feels more like a link between the two other films while "Part III" resurrects the spirit of the first one by focusing on the emotionality rather than the eternal "back to the future" mission. Indeed, as much as I can watch the first one alone, because it's a class on its own and a film I consider slightly independent from the two sequels, on the other hand, I consider the sequels too connected to each other not to be seen in a row. The continuity between the two films is so determining that there's no way watching the second without getting immediately to the third, it's like keeping in touch with the same family. "Back to the Future Part III" was directly made after the second, basically recycling the same material, and using the same team, the same casting etc. As a Sci-Fi Family Romantic Comedy, "Back to the Future Part III" is already a winner, but the Western is the defining aspect of its originality. And here comes the conclusion of one of the finest and most likable cinematic trilogies: "Back to the Future Part III", more than a sequel, a resourcing in the spirit that made the first film such an endearing classic, with an even more escapist value in the setting, the Far West during the 1880's. The radically different 1985 that Marty returns to has thus become an amoral, violent mess with the only solution being another trip back to 1955.
A zip forward into a world of aerial skate boards and self-fastening shoes has unexpectedly disastrous results when the old man version of Biff (Wilson, the bad guy from the first film) borrows the time machine and gives his younger 1955 self a 50-year sports almanac which enables him to bet his way to untold riches, bump off Marty's Pop and not only marry his mom but force her to have breast enlargement surgery. Suddenly hyperactive inventor Doc (Lloyd) is on the scene with the DeLorean time machine warning that Marty's future son needs help in the year 2015. (Fox) just about to give his girlfriend Jennifer (Thompson) a spin in his new pick-up. Emphatically episode two of a three-part serial, this second instalment doesn't make much sense unless you're familiar with the plot of the original film, calling into question as it does all the personal histories so tidily resolved there. The fact that Part II is now being released on video almost simultaneously with Part Ill's theatrical airing simply confirms this. Ending with a big tease sequence of highlights for Back To The Future Part III, this was always going to be the longest movie trailer in Hollywood history.