In Back to the Future Part II, Marty McFly (played by Michael J. Fox) and his eccentric inventor friend Doc Brown (Christopher Lloyd) travel to the year 2015 to prevent Marty's future son from going to jail. However, they discover that Marty's future family is in shambles and his arch-nemesis Biff Tannen (Thomas F. Wilson) has become a wealthy and corrupt businessman thanks to a sports almanac he stole from the future.
Marty and Doc hatch a plan to steal the almanac from Biff's hands before he can use it to alter the future. However, their mission is complicated by the fact that they must avoid being seen by their future selves and the possibility of creating a paradox that could destroy the space-time continuum.
Despite their best efforts, Biff gets his hands on the almanac and uses it to become rich and powerful, creating a dystopian 1985 where he is the ruler of the town. Marty and Doc must travel back to the past and stop Biff from delivering the almanac to his younger self.
As they land in 1955 once again, they find themselves in a race against time as they try to avoid running into their past selves, reunite Marty's parents, and ultimately prevent Biff from using the almanac to alter the future. The film ends with Marty and Doc returning to 1985, where they find that their actions have changed the timeline in unexpected ways and set up the third and final installment in the Back to the Future trilogy.