When we last left our heros 4 years earlier, Doc had just arrived telling Marty and Jennifer that the future of their kids has to be fixed. What's wrong? Well we're about to find out.
Doc, Marty and Jennifer travel to the year 2015! Marty and Jennifer are now married, with two kids. Now there is a problem. One event destroys their family's future, so Marty has to fill in for his son to stop this chain of events. All he has to do is say "No" to everything that Griff Tannen says. Of course though everything goes totally different to plan...
Marty gets called 'chicken' and trys to stop Griff. He doesn't so he takes some girls hoverboard and races away. He gets stuck over some water! Griff lines him up and gets out a baseball bat. He swings at Marty, Marty ducks and Griff and his gang are sent flying into the clocktower! His family is going to be okay.
While this is happening Jennifer has been taken to her future home by the police! Marty and Doc go to find her. They do, but while they get her, Biff Tannen takes the DeLorean and the Sports Almanac (A book that Marty brought containing every result of every major sport from 1950!). Biff has given the book to himself in the past, so he can become rich.
Marty, Doc and Jennifer don't know this and go back to 1985, but soon discover that it's totally different! Biff owns everything! But what's worse is George has been murdered by Biff and Lorraine is now married to Biff instead!
Doc and Marty discover that Biff gave the book to himself in 1955! So they go back and have to get the book, but at the same time not bump into themselves and destroy the events taking place from the first trip! There are now two Doc's and two Marty's in 1955!
They then attempt to steal the almanac from Biff. Instead they steal another magazine. Marty realises that George is about to K.O Biff and runs over and grabs the book. Biff wakes up and chases after Marty. He finds him and takes it back. Marty then goes to Doc and they are going to use the hoverboard to take it back.
Doc lowers Marty down in front of a tunnel and he grabs onto Biffs car. Biff sees him and tries to kill him! Marty grabs the book back. Biff turns the car around and will try to run him over! Just as he's about to hit him Marty grabs onto a rope from Doc. Biff runs into a manure truck!
Marty goes to burn the almanac. He does, then Doc gets hit by lightning! Marty is standing in the rain when a guy comes along in a car. He gives Marty a letter from Doc! He is in 1885! Marty runs back to the main street and finds Doc. He passes out saying "Great Scott!"
