Personally, Back to the Future 3 is my least favourite film in the series. Whilst the first two parts slot together in clever and interesting ways, the final film is much more of a self contained episode and as such feels a little unnecessary. I think the makers were more interested in making a comedy western and this was the ideal opportunity to do so. That’s not to say there isn’t some form of continuity in the films, a good example being Buford “Mad Dog” Tannen (Biff’s great-great(?) grandfather) ending up in a manure cart, recreating the scene from the first film quite nicely where Biff’s car gets a load of the brown stuff dumped on it.
So to the plot. At the end of Part 2 Marty McFly has been left stranded in 1955 when Doc Brown is whisked back in time when the Delorean time machine is struck by lightning. Whilst stood in the rain wondering what to do, a man approaches Marty and hands him an envelope. He is with a messenger firm, and this envelope was left with the company in 1885 under strict instructions to be delivered at a precise time and date in 1955. The envelope is of course from Doc Brown, and it tells Marty where to find the Delorean, which has been hidden for all those years.
After tracking down the car, which has been hidden in a cave, Marty goes about making it time travel worthy again. He also discovers that the Doc was murdered in the past by Buford Tannen, so Marty resolves to go back to 1885 to help the Doc out. After appearing in the middle of a charge of Native Americans, Marty stumbles across his own distant relation, Seamus McFly (also played by Michael J. Fox). Marty finds this out just in time, and decides to go under the moniker of Clint Eastwood instead.
Marty eventually meets up with Doc Brown, who whilst being pleased to see Marty says he is quite happy living in the past in his new role as town Blacksmith. He also hooks up with new school teacher in town Clara Clayton after saving her life, strengthening his desire to remain where he is.
After saving Doc Brown by facing up to Mad Dog and taking him on in the inevitable high noon gun duel, Marty, of course, wants to get back to 1985. Unfortunately the Delorean was damaged so a new way of getting the car up to the requisite speed of 88mph needs to be found. The Doc comes up with a plan to use a steam train to create the necessary speed, so they go about hijacking a train and eventually drive it off an unfinished bridge into a ravine in order to give the car the boost required to travel through time.
All in all the film is still fun, but I think you’ll get more of a kick out of it if you are into Cowboys and Indians style Westerns. It does at least do a reasonably good job of wrapping the trilogy up nicely, and some may find it easier to follow than the multiple timelines presented in part 2.